Recombinant microorganisms and uses therefor

ABSTRACT

The invention provides recombinant microorganisms and methods for the production of acetone from gaseous substrates. For example, the recombinant microorganism may be modified to express an exogenous thiolase, an exogenous CoA transferase, and an exogenous decarboxylase.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/403,972 filed Feb. 23, 2012, which claims the benefit of U.S. Patent Application No. 61/446,832 filed Feb. 25, 2011, the entirety of which are incorporated herein by reference.

FIELD

The present invention relates to methods for the production of acetone, isopropanol and/or a precursor of acetone and/or isopropanol by microbial fermentation of substrates comprising carbon monoxide and genetically modified micro-organisms of use in such methods.

BACKGROUND

Some microorganisms such as Clostridium acetobutylicum or Clostridium beijerinckii are known to produce acetone or isopropanol as major by-products during butanol fermentation (ABE or IBE fermentation) [George H A, Johnson J L, Moore W E C, Holdeman L V, Chen J S: Acetone, isopropanol, and butanol production by Clostridium beijerinckii (syn. Clostridium butylicum) and Clostridium aurantibutyricum. Appl Environ Microbiol 45: 1160-1163]. However, all these organisms rely on sugar or starch based substrates. Acetogenic organisms such as the closely related microorganisms Clostridium autoethanogenum, C. ljungdahlii, and C. ragsdalei are able to grow chemoautotrophically on CO or CO₂/H₂ containing gases as sole energy and carbon source and synthesize products such as acetate, ethanol, or 2,3-butanediol, but neither acetone nor isopropanol [Munasinghe P C, Khanal S K: Biomass-derived syngas fermentation into biofuels: Opportunities and challenges. Bioresource Technol 2010, 5013-22].

Recently, production of isopropanol was reported in a study on Clostridium ragsdalei (Clostridium strain P11) in a 100-L pilot scale fermentor from switchgrass derived syngas [Kundiyana D K, Huhnke R L, Wilkins M R: Syngas fermentation in a 100-L pilot scale fermentor: Design and process considerations. J Biosci Bioeng 2010, 109: 492-498]. However, a related study from the same lab showed that this was due to a contamination in the used syngas since it was passed through a scrubbing mixture containing 20% acetone [Ramachandriya K D: Effect of biomass generated producer gas, methane and physical parameters on producer gas fermentations by Clostridium strain P11. Masters thesis, Oklahoma State University 2009]. The authors also noted that the production of isopropanol may be the result of reduction of propionic acid rather than acetone. Experiments carried out by the inventors of the present invention with Clostridium ragsdalei (Clostridium strain P11) and also C. autoethanogenum and C. ljungdahlii have never shown the production of acetone, isopropanol, or propionic acid.

The cost of many carbohydrate feed stocks suitable for the production of chemical products such as acetone and isoproanol is influenced by their value as human food or animal feed, and the cultivation of starch or sucrose-producing crops for such production is not economically sustainable in all geographies. Therefore, it is of interest to develop technologies to convert lower cost and/or more abundant carbon resources into useful chemical products such as acetone and isopropanol.

CO is a major free energy-rich by-product of the incomplete combustion of organic materials such as coal or oil and oil derived products. For example, the steel industry in Australia is reported to produce and release into the atmosphere over 500,000 tonnes of CO annually.

It is an object of the invention to overcome one or more of the disadvantages of the prior art, or to at least to provide the public with a useful choice.

SUMMARY OF INVENTION

The invention generally provides, inter alia, methods for the production of acetone, isopropanol and/or precursors of acetone and/or isopropanol by microbial fermentation of substrates comprising CO, genetically modified microorganisms of use in such methods, nucleic acids suitable for preparation of genetically modified microorganisms and a novel alcohol dehydrogenase and nucleic acids encoding same.

In a first aspect, the invention provides a carboxydotrophic acetogenic recombinant microorganism capable of producing acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of a substrate comprising CO.

In one particular embodiment, the microorganism is adapted to express one or more enzymes in the isopropanol biosynthesis pathway which are not naturally present in a parental microorganism from which the recombinant microorganism is derived. In another embodiment, the microorganism is adapted to over-express one or more enzymes in the isopropanol biosynthesis pathway which are naturally present in a parental microorganism from which the recombinant microorganism is derived.

In one particular embodiment, the microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway which are not naturally present in a parental microorganism from which the recombinant microorganism is derived. In another embodiment, the microorganism is adapted to over-express one or more enzymes in the acetone biosynthesis pathway which are naturally present in a parental microorganism from which the recombinant microorganism is derived.

In one particular embodiment, the microorganism is adapted to express one or more enzymes involved in the conversion of acetone to isopropanol which are not naturally present in a parental microorganism from which the recombinant microorganism is derived. In another embodiment, the microorganism is adapted to over-express one or more enzymes involved in the conversion of acetone to isopropanol which are naturally present in a parental microorganism from which the recombinant microorganism is derived.

In one embodiment, the parental microorganism is capable of fermenting a substrate comprising CO to produce acetone but not of converting acetone to isopropanol and the recombinant microorganism is adapted to express one or more enzymes involved in the conversion of acetone to isopropanol.

In another embodiment, the parental microorganism is capable of converting acetone to isopropanol but is not capable of fermenting a substrate comprising CO to produce acetone and the recombinant microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway.

In one embodiment, the parental microorganism is not capable of fermenting a substrate comprising CO to produce acetone and isopropanol and the recombinant microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway and one or more enzymes involved in the conversion of acetone to isopropanol.

In one embodiment the one or more enzymes in the isopropanol and/or acetone biosynthesis pathway are chosen from the group consisting:

Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9);

Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9);

Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9);

Acetoacetate decarboxylase (Adc; EC 4.1.1.4);

Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74); and,

A functionally equivalent variant of any one or more thereof.

In one embodiment, the Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) is that derived from C. acetobutylicum.

In one embodiment, the enzymes Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) and Acetoacetate decarboxylase (Adc) are derived from C. beijerinckii.

In one embodiment, the Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) is that derived from Lactococcus lactis.

In one embodiment, the one or more enzyme involved in the conversion of acetone to isopropanol are chosen from the group consisting:

Alcohol Dehydrogenase (Adh; EC 1.1.1.2);

Alcohol dehydrogenase (Adh2; EC 1.1.1.1) and,

A functionally equivalent variant thereof.

In one embodiment, the Alcohol Dehydrogenase (Adh) is derived from C. autoethanogenum, C. ljungdahlii, and/or C. ragsdalei. In one embodiment, the alcohol dehydrogenase has the amino acid sequence of SEQ_ID NO. 1, or it is a functionally equivalent variant thereof. In one embodiment, the functionally equivalent variant has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1.

In one embodiment, the Alcohol Dehydrogenase (Adh2) is derived from S. cerevisiae.

In one embodiment, the microorganism comprises one or more exogenous nucleic acids adapted to increase expression of one or more nucleic acids native to the parental microorganism and which one or more nucleic acids encode one or more of the enzymes referred to herein before.

In one embodiment, the one or more exogenous nucleic acid adapted to increase expression is a regulatory element. In one embodiment, the regulatory element is a promoter. In one embodiment, the promoter is a constitutive promoter. In one embodiment, the promoter is selected from the group comprising Wood-Ljungdahl gene cluster or Phosphotransacetylase/Acetate kinase operon promoters. In one embodiment, the promoter has the sequence of SEQ_ID No. 22 or SEQ ID no. 77, or is a functionally equivalent variant thereof.

In one embodiment, the microorganism comprises one or more exogenous nucleic acids encoding and adapted to express one or more of the enzymes referred to herein before. In one embodiment, the microorganisms comprise one or more exogenous nucleic acid encoding and adapted to express at least two of the enzymes. In other embodiments, the microorganism comprises one or more exogenous nucleic acid encoding and adapted to express 3, 4, 5 or 6 of the enzymes.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), and Acetoacetate decarboxylase (Adc; EC 4.1.1.4) or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exognenous nucleic acids encoding Alcohol Dehydrogenase (Adh; EC 1.1.1.2) or a functionally equivalent variant thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), and Alcohol Dehydrogenase (Adh; EC 1.1.1.2), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), and Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exognenous nucleic acids encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), or a functionally equivalent variant thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In another particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In one embodiment, the nucleic acid encoding Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) comprises the sequence SEQ_ID NO. 18, or a functionally equivalent variant thereof. In one embodiment, the nucleic acid encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) comprises the sequence SEQ_ID NO. 19, or a functionally equivalent variant thereof. In one embodiment, the nucleic acid encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) comprises the sequence SEQ_ID NO. 20, or a functionally equivalent variant thereof. In one embodiment, the nucleic acid encoding Acetoacetate decarboxylase (Adc) comprises the sequence SEQ_ID NO. 21, or a functionally equivalent variant thereof. In one embodiment, the nucleic acid encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) comprises the sequence SEQ_ID NO. 71, or a functionally equivalent variant thereof. In one embodiment, the nucleic acid encoding Alcohol Dehydrogenase (Adh) comprises the sequence SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4, or a functionally equivalent variant of any one thereof. In one embodiment, the functionally equivalent variant of the nucleic acid encoding alcohol dehydrogenase (Adh) has at least approximately 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 2, 3 or 4. In one embodiment, the nucleic acid encoding Alcohol dehydrogenase (Adh2) comprises the sequence SEQ_ID NO. 75, or a functionally equivalent variant thereof.

In one embodiment, the one or more exogenous nucleic acid is a nucleic acid construct or vector, in one particular embodiment a plasmid, encoding one or more of the enzymes referred to hereinbefore in any combination.

In one embodiment, the exogenous nucleic acid is an expression plasmid. In one particular embodiment, the expression plasmid has the nucleotide sequence SEQ_ID No. 46, 48, 83, 84, 95, 98 or 101.

In one embodiment, the parental microorganism is selected from the group of carboxydotrophic acetogenic bacteria selected from the group comprising Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium ragsdalei, Clostridium carboxidivorans, Clostridium drakei, Clostridium scatologenes, Butyribacterium limosum, Butyribacterium methylotrophicum, Acetobacterium woodii, Alkalibaculum bacchii, Blautia producta, Eubacterium limosum, Moorella thermoacetica, Moorella thermautotrophica, Oxobacter pfennigii, and Thermoanaerobacter kiuvi.

In one embodiment the parental microorganism is Clostridium autoethanogenum or Clostridium ljungdahlii. In one particular embodiment, the microorganism is Clostridium autoethanogenum DSM23693. In another particular embodiment, the microorganism is Clostridium ljungdahlii DSM13528 (or ATCC55383).

In one embodiment, the parental microorganism lacks one or more genes encoding ThlA, CtfA, CtfB, Adc, KivD, Adh and Adh2. In one particular embodiment, the parental microorganism lacks a gene encoding Adh. In another particular embodiment, the parental microorganism lacks each of the genes encoding ThlA, CtfA, CtfB, and Adc and KivD.

In second aspect, the invention provides an Alcohol Dehydrogenase (Adh) having the amino acid sequence of SEQ_ID NO. 1, or a functionally equivalent variant of any one thereof.

In one particular embodiment, the functionally equivalent variant of the Alcohol Dehydrogenase (Adh) has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1.

In a third aspect, the invention provides a nucleic acid encoding Adh of SEQ_ID NO. 1 or a functionally equivalent variant thereof.

In a fourth aspect, the invention provides a nucleic acid having the sequence chosen from the group consisting:

SEQ_ID NO. 2

SEQ_ID NO. 3

SEQ_ID NO. 4; and,

A functionally equivalent variant of any one thereof.

In one particular embodiment, a functionally equivalent variant of SEQ_ID NO. 2, 3 or 4 is a nucleic acid at least approximately 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 2, 3 or 4.

In a fifth aspect, the invention provides a nucleic acid capable of hybridising to at least a portion of the nucleic acid SEQ_ID NO. 2, 3 or 4, a nucleic acid complementary to any one thereof, or a functionally equivalent variant of any one thereof.

In a sixth aspect, the invention provides a nucleic acid chosen from the group consisting: SEQ_ID NO. 5; SEQ_ID NO. 6; SEQ_ID NO. 7; SEQ_ID NO. 8; SEQ_ID NO. 9; SEQ_ID NO. 10; SEQ_ID NO. 11; SEQ_ID NO. 12; SEQ_ID NO. 13; SEQ_ID NO. 14; SEQ_ID NO. 15; SEQ_ID NO. 16; SEQ_ID NO. 17; SEQ_ID NO. 18; SEQ_ID NO. 23; SEQ_ID NO. 24; SEQ_ID NO. 25; SEQ_ID NO. 26; SEQ_ID NO. 27; SEQ_ID NO. 28; SEQ_ID NO. 29; SEQ_ID NO. 30; SEQ_ID NO. 31; SEQ_ID NO. 32; SEQ_ID NO. 33; SEQ_ID NO. 64; SEQ_ID NO. 65; SEQ_ID NO. 66; SEQ_ID NO. 67; SEQ_ID NO. 68; SEQ_ID NO. 69; SEQ_ID NO. 70; SEQ_ID NO. 71; SEQ_ID NO. 85; SEQ_ID NO. 86; SEQ_ID NO. 87; SEQ_ID NO. 88; SEQ_ID NO. 89; SEQ_ID NO. 90; SEQ_ID NO. 91; SEQ_ID NO. 92; SEQ_ID NO. 93; SEQ_ID NO. 94; SEQ_ID NO. 96; SEQ_ID NO. 97; SEQ_ID NO. 99; SEQ_ID NO. 100.

In a seventh aspect, the invention provides a nucleic acid encoding one or more enzymes which when expressed in a microorganism allows the microorganism to produce acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of substrate comprising CO.

In one embodiment, the nucleic acid encodes two or more enzymes which when expressed in a microorganism allows the microorganism to produce acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of substrate comprising CO.

In one embodiment, the nucleic acids of the invention encode 3, 4, 5 or 6 such enzymes.

In one embodiment, the enzymes are chosen from Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), Alcohol dehydrogenase (Adh2), Alcohol Dehydrogenase (Adh) and a functionally equivalent variant of any one or more thereof.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), and Acetoacetate decarboxylase (Adc) or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding Alcohol Dehydrogenase (Adh) or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), and Alcohol Dehydrogenase (Adh) or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, the nucleic acid encodes Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) having the sequence of SEQ_ID NO. 42 or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid encodes Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) having the sequence of SEQ_ID NO. 43 or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid encodes Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) having the sequence of SEQ_ID NO 43 and SEQ_ID NO 44, or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid encodes Acetoacetate decarboxylase (Adc) having the sequence of SEQ ID No. 45, or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid encodes Alcohol Dehydrogenase (Adh) having the sequence of SEQ_ID NO 38 and SEQ_ID NO 40. In one particular embodiment, the nucleic acid encodes Alcohol Dehydrogenase (Adh) having the sequence of SEQ_ID NO. 1, or a functionally equivalent variant thereof. In one particular embodiment, the functionally equivalent variant of Alcohol Dehydrogenase (Adh) has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1.

In one embodiment, the nucleic acid encodes Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) having the sequence of SEQ ID No. 73, or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid encodes Alcohol dehydrogenase (Adh2) having the sequence of SEQ ID No. 75, or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) comprises SEQ_ID NO. 18, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) comprises SEQ_ID NO. 19, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) comprises SEQ_ID NO. 20, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Acetoacetate decarboxylase (Adc) comprises SEQ_ID NO. 21, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Alcohol Dehydrogenase (Adh) comprises SEQ_ID NO. 39 or 41. In one particular embodiment, the nucleic acid sequence encoding Alcohol Dehydrogenase (Adh) comprises SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4, or is a functionally equivalent variant of any one thereof. In one embodiment, the functionally equivalent variant of SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4 has at least approximately 83%, 84%, 85%, 86%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 2, 3 or 4.

In one embodiment, the nucleic acid sequence encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) comprises SEQ_ID NO. 72 or 76, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Alcohol dehydrogenase (Adh2) comprises SEQ_ID NO. 74 or 77, or is a functionally equivalent variant thereof.

In one embodiment, the nucleic acids of the invention further comprise a promoter. In one embodiment, the promoter allows for constitutive expression of the genes under its control. In a particular embodiment a Wood-Ljungdahl cluster promoter is used. In another particular embodiment, a Phosphotransacetylase/Acetate kinase operon promoter is used. In one particular embodiment, the promoter is from C. autoethanogenum. In one particular embodiment, the promoter has the sequence of SEQ_ID NO. 22, SEQ_ID NO. 79, or is a functionally equivalent variant thereof.

In an eighth aspect, the invention provides a nucleic acid construct or vector comprising one or more nucleic acid of the seventh aspect.

In one particular embodiment, the nucleic acid construct or vector is an expression construct or vector. In one particular embodiment, the expression construct or vector is a plasmid. In one particular embodiment, the expression plasmid has the nucleotide sequence SEQ_ID No. 46, 47, 48, 83, 84, 95, 98 or 101.

In a ninth aspect, the invention provides host organisms comprising any one or more of the nucleic acids of the seventh aspect or vectors or constructs of the eighth aspect.

In a tenth aspect, the invention provides a composition comprising an expression constructor vector as referred to in the eighth aspect of the invention and a methylation construct or vector.

Preferably, the composition is able to produce a recombinant microorganism according to the first aspect of the invention.

In one particular embodiment, the expression construct/vector and/or the methylation construct/vector is a plasmid.

In an eleventh aspect, the invention provides a method of producing a recombinant microorganism of the invention comprising:

-   -   a) introduction into a shuttle microorganism of (i) an         expression construct/vector of the eighth aspect of the         invention and (ii) a methylation construct/vector comprising a         methyltransferase gene;     -   b) expression of the methyltransferase gene;     -   c) isolation of one or more constructs/vectors from the shuttle         microorganism; and,     -   d) introduction of at least the expression construct/vector into         a destination microorganism.

In one embodiment, both the methyltransferase gene of step B is expressed constitutively. In another embodiment, expression of the methyltransferase gene of step B is induced.

In one embodiment, both the methylation construct/vector and the expression construct/vector are isolated in step C. In another embodiment, only the expression construct/vector is isolated in step C.

In one embodiment, only the expression construct/vector is introduced into the destination microorganism. In another embodiment, both the expression construct/vector and the methylation construct/vector are introduced into the destination microorganism.

In a related aspect, the invention provides a method of producing a recombinant microorganism of the invention comprising:

-   -   a. methylation of an expression construct/vector of the eighth         aspect of the invention in vitro by a methyltransferase;     -   b. introduction of the expression construct/vector into a         destination microorganism.

In a further related aspect, the invention provides a method of producing a recombinant microorganism of the invention comprising:

-   -   a. introduction into the genome of a shuttle microorganism of a         methyltransferase gene     -   b. introduction of an expression construct/vector of the eighth         aspect of the invention into the shuttle microorganism     -   c. isolation of one or more constructs/vectors from the shuttle         microorganism; and,     -   d. introduction of at least the expression construct/vector into         a destination microorganism.

In a twelfth aspect, the invention provides a method for the production of acetone, isopropanol, and/or a precursor of acetone and/or isopropanol by microbial fermentation comprising fermenting a substrate comprising CO using a recombinant microorganism of the first aspect of the invention.

In one embodiment the method comprises the steps of:

-   -   (a) providing a substrate comprising CO to a bioreactor         containing a culture of one or more microorganism of the first         aspect of the invention; and     -   (b) anaerobically fermenting the culture in the bioreactor to         produce acetone, isopropanol, and/or a precursor of acetone         and/or isopropanol.

In one embodiment the method comprises the steps of:

-   -   (a) capturing CO-containing gas produced as a result of the         industrial process, before the gas is released into the         atmosphere;     -   (b) the anaerobic fermentation of the CO-containing gas to         produce acetone, isopropanol, and/or a precursor acetone and/or         isopropanol by a culture containing one or more microorganism of         the first aspect of the invention.

In particular embodiments of the method aspects, the microorganism is maintained in an aqueous culture medium.

In particular embodiments of the method aspects, the fermentation of the substrate takes place in a bioreactor.

Preferably, the substrate comprising CO is a gaseous substrate comprising CO. In one embodiment, the substrate comprises an industrial waste gas. In certain embodiments, the gas is steel mill waste gas or syngas.

In one embodiment, the substrate will typically contain a major proportion of CO, such as at least about 20% to about 100% CO by volume, from 20% to 70% CO by volume, from 30% to 60% CO by volume, and from 40% to 55% CO by volume. In particular embodiments, the substrate comprises about 25%, or about 30%, or about 35%, or about 40%, or about 45%, or about 50% CO, or about 55% CO, or about 60% CO by volume.

In certain embodiments the methods further comprise the step of recovering one or more of acetone, isopropanol, and/or a precursor of acetone and/or isopropanol from the fermentation broth, the fermentation broth.

In a thirteenth aspect, the invention provides one or more of acetone, isopropanol, and a precursor of acetone and/or isopropanol when produced by the method of the sixth aspect.

In another aspect, the invention provides a method for the production of a microorganism of the first aspect of the invention comprising transforming a carboxydotrophic acetogenic parental microorganism with one or more exogenous nucleic acid such that the microorganism is capable of producing acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of a substrate comprising CO, wherein the parental microorganism is not capable of producing acetone, isopropanol and/or a precursor thereof by fermentation of a substrate comprising CO.

In one particular embodiment, a parental microorganism is transformed with one or more exogenous nucleic acid adapted to express one or more enzymes in the isopropanol biosynthesis pathway which are not naturally present in the parental microorganism. In another embodiment, a parental microorganism is transformed with one or more nucleic acid adapted to over-express one or more enzymes in the isopropanol biosynthesis pathway which are naturally present in the parental microorganism.

In one particular embodiment, a parental microorganism is transformed with one or more exogenous nucleic acids adapted to express one or more enzymes in the acetone biosynthesis pathway which are not naturally present in the parental microorganism. In another embodiment, a parental microorganism is transformed with one or more exogenous nucleic acids adapted to over-express one or more enzymes in the acetone biosynthesis pathway which are naturally present in the parental microorganism.

In one particular embodiment, a parental microorganism is transformed with one or more nucleic acid adapted to express one or more enzymes involved in the conversion of acetone to isopropanol which are not naturally present in the parental microorganism. In another embodiment, a parental microorganism is transformed with one or more nucleic acids adapted to over-express one or more enzymes involved in the conversion of acetone to isopropanol which are naturally present in the parental microorganism.

In certain embodiments, the one or more enzymes are as herein before described.

In another aspect, the invention provides a recombinant microorganism capable of producing acetone and comprising one or more exogenous nucleic acid encoding one or more enzyme adapted to convert acetoactate to acetone, wherein the recombinant microorganism is derived from a parental microorganism which is capable of producing acetolactate but not acetone. In one embodiment, one or more enzyme comprises KivD or a functionally equivalent variant thereof.

In another aspect, the invention provides a recombinant microorganism capable of producing acetone and comprising one or more exogenous nucleic acid encoding each of the enzymes thlA, ctfA, ctfB and kivD or a functionally equivalent variant of any one or more thereof, wherein the recombinant microorganism is derived from a parental microorganism which is not capable of producing acetolactate, acetoacetyl-CoA and acetone.

In another aspect, the invention provides a recombinant microorganism capable of producing acetone and comprising one or more exogenous nucleic acid encoding each of the enzymes ctfA, ctfB and kivD or a functionally equivalent variant of any one or more thereof, wherein the recombinant microorganism is derived from a parental microorganism which is not capable of producing acetolactate and acetone.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which the invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth.

BRIEF DESCRIPTION OF THE FIGURES

These and other aspects of the present invention, which should be considered in all its novel aspects, will become apparent from the following description, which is given by way of example only, with reference to the accompanying figures, in which:

FIG. 1 shows amino acid alignment of novel alcohol dehydrogenase of C. autoethanogenum (CAU) (SEQ ID NO: 1), C. ljungdahlii (CU) (SEQ ID NO: 1), and C. ragsdalei (CRA) (SEQ ID NO: 1) with the secondary alcohol dehydrogenase of C. beijerinckii strain NRRL-B593 (SEQ ID NO: 38).

FIG. 2 show expression of novel alcohol dehydrogenase gene of Clostridium autoethanogenum DSM23693 during a typical fermentation run, as well as expression of genes controlled by Wood-Ljungdahl operon promoter, F₁F_(o) ATPase operon promoter, Rnf complex operon promoter, and Pyruvate:ferredoxin oxidoreductase promoter. mRNA levels of more than 200 genes of interest were compared.

FIG. 3 shows acetone expression plasmid pMTL85147-thlA-ctfA-ctfB-adc.

FIG. 4 shows the pathway for production of acetone and isopropanol from CO or CO/H₂ containing gases in engineered C. autoethanogenum and C. ljungdahlii carrying plasmid pMTL85147-thlA-ctfA-ctfB-adc.

FIG. 5 shows the sequencing results of acetone expression plasmid pMTL85147-thlA-ctfA-ctfB-adc.

FIG. 6 illustrates the designed methylation plasmid.

FIG. 7 shows detection of ctfAB-adc (2.2 kb) from PCR of plasmids isolated from transformed C. autoethanogenum DSM23693 and C. ljungdahlii DSM13528. Ladder=1 KB Plus DNA ladder (Invitrogen); 1=non-template control; 2=plasmid isolated from C. autoethanogenum; 3=plasmid isolated from C. ljungdahlii; 4=original pMTL85147-thlA-ctfAB-adc (positive control).

FIG. 8 shows the result of growth experiments with C. autoethanogenum DSM23693+pMTL85147-thlA-ctfAB-adc on steel mill gas.

FIG. 9 shows the result of growth experiments with C. ljungdahlii DSM13528+pMTL85147-thlA-ctfAB-adc on steel mill gas.

FIG. 10 shows the GC result confirming acetone production with C. autoethanogenum DSM13528+pMTL85147-thlA-ctfAB-adc (top) and C. ljungdahlii DSM13528+pMTL85147-thlA-ctfAB-adc (bottom) from steel mill gas.

FIG. 11 shows the GC result confirming acetone production with C. autoethanogenum DSM23693+pMTL85147-thlA-ctfAB-adc from syngas.

FIG. 12 shows the toxicity of acetone on cultures of C. autoethanogenum DSM23693.

FIG. 13 shows the toxicity of isopropanol on cultures of C. autoethanogenum DSM23693.

FIG. 14 shows SEQ_ID NO 1: Amino acid sequence of novel alcohol dehydrogenase from C. autoethanogeum, C. ljungdahlii and C. ragsdalei.

FIG. 15 shows SEQ_ID NO 2: Nucleic acid sequence of novel alcohol dehydrogenase gene from C. autoethanogeum.

FIG. 16 shows SEQ_ID NO 3: Nucleic acid sequence of novel alcohol dehydrogenase gene from C. ljungdahlii.

FIG. 17 shows SEQ_ID NO 4: Nucleic acid sequence of novel alcohol dehydrogenase gene from C. ragsdalei.

FIG. 18 shows SEQ_ID NO 18: Nucleic acid sequence of Thiolase gene (thlA) from C. acetobutylicum ATCC824.

FIG. 19 shows SEQ_ID NO 19: Nucleic acid sequence of Acetoacetyl-CoA:acetate Coenzyme A transferase A (ctfA) gene from C. beijerinckii NCIMB8052.

FIG. 20 shows SEQ_ID NO 20: Nucleic acid sequence of Acetoacetyl-CoA:acetate Coenzyme A transferase B (ctfB) gene from C. beijerinckii NCIMB8052.

FIG. 21 shows SEQ_ID NO 21: Nucleic acid sequence of Acetoacetate decarboxylase (adc) gene from C. beijerinckii NCIMB8052.

FIG. 22 shows SEQ_ID NO 22: Nucleic acid sequence of Wood-Ljungdahl cluster promoter (P_(WL)) from C. autoethanogenum.

FIG. 23 shows SEQ_ID NO 34: Amino acid sequence of designed Type II methyltransferase gene.

FIG. 24 shows SEQ_ID NO 35: Nucleic acid sequence of designed Type II methyltransferase gene.

FIG. 25 shows SEQ_ID NO 38: Amino acid sequence of NADP-dependent alcohol dehydrogenase from Clostridium beijerinckii NRRL B-593.

FIG. 26 shows SEQ_ID NO 39: Nucleic acid sequence of NADP-dependent alcohol dehydrogenase from Clostridium beijerinckii NRRL B-593.

FIG. 27 shows SEQ_ID NO 40: Amino acid sequence of NADP-dependent alcohol dehydrogenase from Thermoanaerobacter brockii ATCC 53556.

FIG. 28 shows SEQ_ID NO 41: Nucleic acid sequence of alcohol dehydrogenase from Thermoanaerobacter brockii.

FIG. 29 shows SEQ_ID NO 42: Amino acid sequence of Thiolase ThlA from C. acetobutylicum ATCC824.

FIG. 30 shows SEQ_ID NO 43: Amino acid sequence of Acetoacetyl-CoA:acetate Coenzyme A transferase A CtfA from C. beijerinckii NCIMB8052.

FIG. 31 shows SEQ_ID NO 44: Amino acid sequence of Acetoacetyl-CoA:acetate Coenzyme A transferase A CtfB from C. beijerinckii NCIMB8052.

FIG. 32 shows SEQ_ID NO 45: Amino acid sequence of Acetoacetate decarboxylase Adc from C. beijerinckii NCIMB8052.

FIG. 33 shows SEQ_ID NO 46: Nucleic acid sequence of expression plasmid containing novel alcohol dehydrogenase pMTL85147-thlA-ctfAB-adc.

FIG. 34 shows SEQ_ID NO 47: Nucleic acid sequence of Acetoacetyl-CoA:acetate Coenzyme A transferase A (ctfA), acetoacetyl-CoA:acetate Coenzyme A transferase B (ctfB), and acetoacetate decarboxylase (adc) operon of C. beijerinckii.

FIG. 35 shows SEQ_ID NO 48: Nucleic acid sequence of expression plasmid containing novel alcohol dehydrogenase pMTL85147-thlA-ctfAB-adc-adh.

FIG. 36 shows SEQ_ID NO 49: Nucleic acid sequence of designed methylation plasmid.

FIG. 37 shows SEQ_ID NO 50: Nucleic acid sequence of lac promoter.

FIG. 38 shows SEQ_ID NO 51: Nucleic acid sequence of Clostridium autoethanogenum F₁F_(o) ATPase operon promoter region.

FIG. 39 shows SEQ_ID NO 52: Nucleic acid sequence of Clostridium autoethanogenum Rnf complex operon promoter region.

FIG. 40 shows SEQ_ID NO 53: Nucleic acid sequence of Clostridium autoethanogenum Pyruvate:ferredoxin oxidoreductase promoter region.

FIG. 41 shows the sequencing results of expression plasmid containing novel alcohol dehydrogenase pMTL85147-thlA-ctfA-ctfB-adc-adh.

FIG. 42 shows the results of acetone and isopropanol production with E. coli XL-1 Blue MRF′ Kan carrying control plasmid (pMTL85147), acetone expression plasmid (pMTL85147-thlA-ctfA-ctfB-adc), and acetone expression plasmid including the novel alcohol dehydrogaenase (pMTL85147-thlA-ctfA-ctfB-adc-adh).

FIG. 43 shows expression plasmid containing novel alcohol dehydrogenase pMTL85147-thlA-ctfA-ctfB-adc-adh.

FIG. 44 shows SEQ_ID NO 56: Nucleic acid sequence of Wood-Ljungdahl cluster promoter (P_(WL)) from C. ljungdahlii.

FIG. 45 shows SEQ_ID NO 57: Nucleic acid sequence of Wood-Ljungdahl cluster promoter (P_(WL)) from C. ragsdalei.

FIG. 46 shows SEQ_ID NO 58: Nucleic acid sequence of Clostridium ljungdahlii F₁F_(o) ATPase operon promoter region.

FIG. 47 shows SEQ_ID NO 59: Nucleic acid sequence of Clostridium ragsdalei F₁F_(o) ATPase operon promoter region.

FIG. 48 shows SEQ_ID NO 60: Nucleic acid sequence of Clostridium ljungdahlii Rnf complex operon promoter region.

FIG. 49 shows SEQ_ID NO 61: Nucleic acid sequence of Clostridium ragsdalei Rnf complex operon promoter region.

FIG. 50 shows SEQ_ID NO 62: Nucleic acid sequence of Clostridium ljungdahlii Pyruvate:ferredoxin oxidoreductase promoter region.

FIG. 51 shows SEQ_ID NO 63: Nucleic acid sequence of Clostridium ragsdalei Pyruvate:ferredoxin oxidoreductase promoter region.

FIG. 52 shows qRT-PCR amplification plot confirming amplification of probes for heterologous genes thlA, ctfA, ctfB, and adc in Clostridium autoethanogenum harbouring plasmid pMTL85147-thlA-ctfAB-adc

FIG. 53 shows qRT-PCR amplification plot confirming amplification of probes for heterologous genes thlA, ctfA, ctfB, and adc in Clostridium ljungdahlii harbouring plasmid pMTL85147-thlA-ctfAB-adc

FIG. 54 shows SEQ_ID No. 73: Amino acid sequence of alpha-ketoisovalerate decarboxylase KivD from Lactococcus lactis KF147 and SEQ_ID No. 72 Nucleic acid sequence of Alpha-ketoacid decarboxylase (kivd).

FIG. 55 shows Seq. ID No. 76: Codon optimized sequence of Alpha-ketoacid decarboxylase (kivd), SEQ_ID No. 75: Amino acid sequence of alcohol dehydrogenase Adh2 from Saccharomyces cerevisiae and SEQ_ID No. 74 Nucleic acid sequence of Alcohol dehydrogenase (adh2)

FIG. 56 shows Seq. ID No. 78: Synthetic operon of codon optimized Alpha-ketoacid decarboxylase (kivd) and Alcohol dehydrogenase (Adh2) including spacer sequence with ribosomal binding site, flanked by NdeI and KpnI and Seq. ID No. 77: Codon optimized sequence of Alcohol dehydrogenase (Adh2).

FIG. 57 shows SEQ_ID No. 82: Nucleic acid sequence of E. coli-Clostridium shuttle vector pMTL 85245 and SEQ_ID No. 79: Nucleic acid sequence of Phosphotransacetylase Acetate kinase promoter from C. autoethanogenum,

FIG. 58 shows SEQ_ID No. 83: Nucleic acid sequence of expression plasmid pMTL85245-kivd-adh2

FIG. 59 shows SEQ_ID No. 84 Nucleic acid sequence of expression plasmid pMTL85245-kivd

FIG. 60 shows SEQ_ID No. 93: Nucleic acid sequence of expression plasmid pMTL85245-P-thl-ctfAB-P-kivd

FIG. 61 shows SEQ_ID No. 98 Nucleic acid sequence of expression plasmid pMTL83147-thlA-ctfAB-adc-adh2.

FIG. 62 shows SEQ_ID No. 101 Nucleic acid sequence of expression plasmid pMTL83147-thlA-ctfAB-adc-P-kivd-adh2.

FIG. 63 shows acetone expression plasmid pMTL85245-kivd-adh2

FIG. 64 shows acetone expression plasmid pMTL85245-kivd

FIG. 65 shows the GC result confirming acetone and isopropanol production with C. autoethanogenum DSM23693 as a control strain (top) and C. autoethanogenum DSM23693+pMTL85245-kivd-adh2 (bottom) from CO-containing steel mill gas.

FIG. 66 shows the GC result confirming acetone and isopropanol production with C. autoethanogenum DSM23693+pMTL85245-kivd from CO-containing steel mill gas.

FIG. 67 shows acetone expression plasmid pMTL85147-thlA-ctfA-ctfB-adc-P-kivd

FIG. 68 shows acetone expression plasmid pMTL83147-thlA-ctfA-ctfB-adc-adh

FIG. 69 shows acetone expression plasmid pMTL83147-thlA-ctfA-ctfB-adc-P-kivd-adh

FIG. 70 shows the GC result confirming acetone and isopropanol production with C. autoethanogenum DSM23693 (top) and C. autoethanogenum DSM23693+pMTL85245-Pwl-thlA-ctfAB-kivd from CO-containing steel mill gas.

FIG. 71 shows shows the GC result confirming acetone and isopropanol production with C. autoethanogenum DSM23693+pMTL83147-thlA-ctfAB-adc-adh2 from CO-containing steel mill gas.

FIG. 72 shows the GC result confirming acetone and isopropanol production with C. autoethanogenum DSM23693+pMTL83147-thlA-ctfAB-adc-P-kivd-adh2 from CO-containing steel mill gas.

FIG. 73 shows tested gene combinations of Clostridial pathway genes and codon-optimized Alpha-ketoacid decarboxylase Kivd from L lactis and Alcohol dehydrogenase Adh2 from S. cerevisiae heterologously expressed in E. coli and C. autoethanogenum.

FIG. 74 shows complete conversion of acetone to isopropanol at high concentrations and rates when fed into a stable continuous culture of C. autoethanogenum DSM23693 with CO-containing steel mill gas as substrate.

DETAILED DESCRIPTION OF THE INVENTION

The following is a description of the present invention, including preferred embodiments thereof, given in general terms. The invention is further elucidated from the disclosure given under the heading “Examples” herein below, which provides experimental data supporting the invention, specific examples of various aspects of the invention, and means of performing the invention.

The production of acetone and/or isopropanol by microbial fermentation of substrates comprising CO has not previously been reported. The inventors of the present invention have now demonstrated (inter alia), through genetic modification, the production of acetone and isopropanol in species of carboxydotrophic acetogenic bacteria capable of using CO as a carbon and energy source. The inventors have also surprisingly been able to demonstrate the natural enzymatic conversion of acetone to isopropanol in presence of CO-containing gases by closely related carboxydotrophic acetogenic species C. autoethanogenum, C. ljungdahlii, and C. ragsdalei. A novel alcohol dehydrogenase was identified, which was shown to be expressed constitutively at a high level during a normal fermentation run with C. autoethanogenum and is able to convert acetone to isopropanol at high concentrations and ratios. The inventors have also found two genes that surprisingly confer activity towards acetone and isopropanol in C. autoethanogenum. These genes, an alpha-ketoacid decarboxylase (Kivd) from Lactococcus lactis and an alcohol dehydrogenase (Adh2) from Saccharomyces cerevisiae haven't been reported to confer activity towards acetone or isopropanol or any of it's precursors, rather converting amino acid precursors into branched chain alcohols. The inventors demonstrated production of acetone and isopropanol from CO in C. autoethanogenum using several different gene and enzyme combinations.

Accordingly, the invention provides, for example, methods for the production of acetone, isopropanol and/or precursors of acetone and/or isopropanol by microbial fermentation of substrates comprising CO, genetically modified microorganisms of use in such methods, nucleic acids suitable for preparation of genetically modified microorganisms and novel alcohol dehydrogenases and nucleic acids encoding same.

As referred to herein, a “fermentation broth” is a culture medium comprising at least a nutrient media and bacterial cells.

As referred to herein, a shuttle microorganism is a microorganism in which a methyltransferase enzyme is expressed and is distinct from the destination microorganism.

As referred to herein, a destination microorganism is a microorganism in which the genes included on an expression construct/vector are expressed and is distinct from the shuttle microorganism.

The term “main fermentation product” is intended to mean the one fermentation product which is produced in the highest concentration and/or yield.

The terms “increasing the efficiency”, “increased efficiency” and the like, when used in relation to a fermentation process, include, but are not limited to, increasing one or more of the rate of growth of microorganisms catalysing the fermentation, the growth and/or product production rate at elevated acetone and/or isopropanol concentrations, the volume of desired product produced per volume of substrate consumed, the rate of production or level of production of the desired product, and the relative proportion of the desired product produced compared with other by-products of the fermentation.

The phrase “substrate comprising carbon monoxide” and like terms should be understood to include any substrate in which carbon monoxide is available to one or more strains of bacteria for growth and/or fermentation, for example.

The phrase “gaseous substrate comprising carbon monoxide” and like phrases and terms includes any gas which contains a level of carbon monoxide. In certain embodiments the substrate contains at least about 20% to about 100% CO by volume, from 20% to 70% CO by volume, from 30% to 60% CO by volume, and from 40% to 55% CO by volume. In particular embodiments, the substrate comprises about 25%, or about 30%, or about 35%, or about 40%, or about 45%, or about 50% CO, or about 55% CO, or about 60% CO by volume.

While it is not necessary for the substrate to contain any hydrogen, the presence of H₂ should not be detrimental to product formation in accordance with methods of the invention. In particular embodiments, the presence of hydrogen results in an improved overall efficiency of alcohol production. For example, in particular embodiments, the substrate may comprise an approx 2:1, or 1:1, or 1:2 ratio of H₂:CO. In one embodiment the substrate comprises about 30% or less H₂ by volume, 20% or less H₂ by volume, about 15% or less H₂ by volume or about 10% or less H₂ by volume. In other embodiments, the substrate stream comprises low concentrations of H₂, for example, less than 5%, or less than 4%, or less than 3%, or less than 2%, or less than 1%, or is substantially hydrogen free. The substrate may also contain some CO₂ for example, such as about 1% to about 80% CO₂ by volume, or 1% to about 30% CO₂ by volume. In one embodiment the substrate comprises less than or equal to about 20% CO₂ by volume. In particular embodiments the substrate comprises less than or equal to about 15% CO₂ by volume, less than or equal to about 10% CO₂ by volume, less than or equal to about 5% CO₂ by volume or substantially no CO₂.

In the description which follows, embodiments of the invention are described in terms of delivering and fermenting a “gaseous substrate containing CO”. However, it should be appreciated that the gaseous substrate may be provided in alternative forms. For example, the gaseous substrate containing CO may be provided dissolved in a liquid. Essentially, a liquid is saturated with a carbon monoxide containing gas and then that liquid is added to the bioreactor. This may be achieved using standard methodology. By way of example, a microbubble dispersion generator (Hensirisak et. al. Scale-up of microbubble dispersion generator for aerobic fermentation; Applied Biochemistry and Biotechnology Volume 101, Number 3/October, 2002) could be used. By way of further example, the gaseous substrate containing CO may be adsorbed onto a solid support. Such alternative methods are encompassed by use of the term “substrate containing CO” and the like.

In particular embodiments of the invention, the CO-containing gaseous substrate is an industrial off or waste gas. “Industrial waste or off gases” should be taken broadly to include any gases comprising CO produced by an industrial process and include gases produced as a result of ferrous metal products manufacturing, non-ferrous products manufacturing, petroleum refining processes, gasification of coal, gasification of biomass, electric power production, carbon black production, and coke manufacturing. Further examples may be provided elsewhere herein.

Unless the context requires otherwise, the phrases “fermenting”, “fermentation process” or “fermentation reaction” and the like, as used herein, are intended to encompass both the growth phase and product biosynthesis phase of the process. As will be described further herein, in some embodiments the bioreactor may comprise a first growth reactor and a second fermentation reactor. As such, the addition of metals or compositions to a fermentation reaction should be understood to include addition to either or both of these reactors.

The term “bioreactor” includes a fermentation device consisting of one or more vessels and/or towers or piping arrangement, which includes the Continuous Stirred Tank Reactor (CSTR), Immobilized Cell Reactor (ICR), Trickle Bed Reactor (TBR), Bubble Column, Gas Lift Fermenter, Static Mixer, or other vessel or other device suitable for gas-liquid contact. In some embodiments the bioreactor may comprise a first growth reactor and a second fermentation reactor. As such, when referring to the addition of substrate to the bioreactor or fermentation reaction it should be understood to include addition to either or both of these reactors where appropriate.

“Exogenous nucleic acids” are nucleic acids which originate outside of the microorganism to which they are introduced. Exogenous nucleic acids may be derived from any appropriate source, including, but not limited to, the microorganism to which they are to be introduced, strains or species of microorganisms which differ from the organism to which they are to be introduced, or they may be artificially or recombinantly created. In one embodiment, the exogenous nucleic acids represent nucleic acid sequences naturally present within the microorganism to which they are to be introduced, and they are introduced to increase expression of or over-express a particular gene (for example, by increasing the copy number of the sequence (for example a gene), or introducing a strong or constitutive promoter to increase expression). In another embodiment, the exogenous nucleic acids represent nucleic acid sequences not naturally present within the microorganism to which they are to be introduced and allow for the expression of a product not naturally present within the microorganism or increased expression of a gene native to the microorganism (for example in the case of introduction of a regulatory element such as a promoter). The exogenous nucleic acid may be adapted to integrate into the genome of the microorganism to which it is to be introduced or to remain in an extra-chromosomal state.

It should be appreciated that the invention may be practiced using nucleic acids whose sequence varies from the sequences specifically exemplified herein provided they perform substantially the same function. For nucleic acid sequences that encode a protein or peptide this means that the encoded protein or peptide has substantially the same function. For nucleic acid sequences that represent promoter sequences, the variant sequence will have the ability to promote expression of one or more genes. Such nucleic acids may be referred to herein as “functionally equivalent variants”. By way of example, functionally equivalent variants of a nucleic acid include allelic variants, fragments of a gene, genes which include mutations (deletion, insertion, nucleotide substitutions and the like) and/or polymorphisms and the like. Homologous genes from other microorganisms may also be considered as examples of functionally equivalent variants of the sequences specifically exemplified herein. These include homologous genes in species such as Clostridium acetobutylicum, Clostridium beijerinckii, C. saccharobutylicum and C. saccharoperbutylacetonicum, details of which are publicly available on websites such as Genbank or NCBI. In the case of genes derived from Saccharomyces cerevisiae and Lactococcus lactics, homologous genes may be found, for example, in Staphylococcus epidermidis (for example, NP_765765.1, EGG67352.1, ZP_04826144.1, ZP_04797999.1), Bacillus cereus (for example, ZP_04273468.1, ZP_04317620.1) and Bacillus thuringiensis (for example, YP_003664720.1). The phrase “functionally equivalent variants” should also be taken to include nucleic acids whose sequence varies as a result of codon optimisation for a particular organism. “Functionally equivalent variants” of a nucleic acid herein will preferably have at least approximately 70%, preferably approximately 80%, more preferably approximately 85%, preferably approximately 90%, preferably approximately 95% or greater nucleic acid sequence identity with the nucleic acid identified.

It should also be appreciated that the invention may be practiced using polypeptides whose sequence varies from the amino acid sequences specifically exemplified herein. These variants may be referred to herein as “functionally equivalent variants”. A functionally equivalent variant of a protein or a peptide includes those proteins or peptides that share at least 40%, preferably 50%, preferably 60%, preferably 70%, preferably 75%, preferably 80%, preferably 85%, preferably 90%, preferably 95% or greater amino acid identity with the protein or peptide identified and has substantially the same function as the peptide or protein of interest. Such variants include within their scope fragments of a protein or peptide wherein the fragment comprises a truncated form of the polypeptide wherein deletions may be from 1 to 5, to 10, to 15, to 20, to 25 amino acids, and may extend from residue 1 through 25 at either terminus of the polypeptide, and wherein deletions may be of any length within the region; or may be at an internal location. Functionally equivalent variants of the specific polypeptides herein should also be taken to include polypeptides expressed by homologous genes in other species of bacteria, for example as exemplified in the previous paragraph.

“Substantially the same function” as used herein is intended to mean that the nucleic acid or polypeptide is able to perform the function of the nucleic acid or polypeptide of which it is a variant. For example, a variant of an enzyme of the invention will be able to catalyse the same reaction as that enzyme. However, it should not be taken to mean that the variant has the same level of activity as the polypeptide or nucleic acid of which it is a variant.

One may assess whether a functionally equivalent variant has substantially the same function as the nucleic acid or polypeptide of which it is a variant using any number of known methods. However, by way of example, the methods outlined in Wiesenborn et al [Thiolase from Clostridium acetobutylicum ATCC 824 and Its Role in the Synthesis of Acids and Solvents. Appl Environ Microbiol. 1988, 54: 2717-2722], Wiesenborn et al [Coenzyme A transferase from Clostridium acetobutylicum ATCC 824 and its role in the uptake of acids. Appl Environ Microbiol. 1989, 55:323-9.], Peterson and Bennet [Purification of acetoacetate decarboxylase from Clostridium acetobutylicum ATCC 824 and cloning of the acetoacetate decarboxylase gene in Escherichia coli. Appl Environ Microbiol. 1990 56: 3491-3498], Ismail et al. [Purification and characterization of a primary-secondary alcohol dehydrogenase from two strains of Clostridium beijerinckii. J Bacteriol 1993, 175: 5097-5105], de la Plaza et al [Biochemical and molecular characterization of a-ketoisovalerate decarboxylase, an enzyme involved in the formation of aldehydes from amino acids by Lactococcus lactis. FEMS Microbiol Lett. 2004 238: 367-374] or Khorkin et al [NADP-dependent bacterial alcohol dehydrogenases: crystal structure, cofactor-binding and cofactor specificity of the ADHs of Clostridium beijerinckii and Thermoanaerobacter brockii. J Mol Biol. 1998, 22: 278(5): 967-981] may be used to assess enzyme activity.

“Over-express”, “over expression” and like terms and phrases when used in relation to the invention should be taken broadly to include any increase in expression of one or more protein as compared to the expression level of the protein of a parental microorganism under the same conditions. It should not be taken to mean that the protein is expressed at any particular level.

A “parental microorganism” is a microorganism used to generate a recombinant microorganism of the invention. The parental microorganism may be one that occurs in nature (i.e. a wild type microorganism) or one that has been previously modified but which does not express or over-express one or more of the enzymes the subject of the present invention. Accordingly, the recombinant microorganisms of the invention have been modified to express or over-express one or more enzymes that were not expressed or over-expressed in the parental microorganism.

The terms nucleic acid “constructs” or “vectors” and like terms should be taken broadly to include any nucleic acid (including DNA and RNA) suitable for use as a vehicle to transfer genetic material into a cell. The terms should be taken to include plasmids, viruses (including bacteriophage), cosmids and artificial chromosomes. Constructs or vectors may include one or more regulatory elements, an origin of replication, a multicloning site and/or a selectable marker. In one particular embodiment, the constructs or vectors are adapted to allow expression of one or more genes encoded by the construct or vector. Nucleic acid constructs or vectors include naked nucleic acids as well as nucleic acids formulated with one or more agents to facilitate delivery to a cell (for example, liposome-conjugated nucleic acid, an organism in which the nucleic acid is contained).

The “isopropanol biosynthesis pathway” is the enzymatic pathway allowing for metabolism of CO or CO/H₂ to isopropanol, as outlined, for example, in FIG. 4.

The “acetone biosynthesis pathway” is the enzymatic pathway allowing for metabolism of CO or CO/H₂ to acetone, as outlined, for example, in FIG. 4.

A “precursor” of acetone includes Acetyl-CoA, Acetoacetyl-CoA, Acetoacetate, Acetyl-Phosphate and Acetic Acid.

A “precursor” of isopropanol includes Acetyl-CoA, Acetoacetyl-CoA, Acetoacetate, Acetone, Acetyl-Phosphate and Acetic Acid.

Reference to “alcohol dehydrogenases” should be taken to include alcohol dehydrogenases which are capable of catalysing the conversion of ketones (such as acetone) to secondary alcohols (such as isopropanol), or vice versa. Such alcohol dehydrogenases include secondary alcohol dehydrogenases and primary alcohol dehydrogenases. A “secondary alcohol dehydrogenase” is one which can convert ketones (such as acetone) to secondary alcohols (such as isopropanol), or vice versa. A “primary alcohol dehydrogenase” is one which can convert aldehydes to primary alcohols, or vice versa; however, a number of primary alcohol dehydrogenases are also capable of catalysing the conversion of ketones to secondary alcohols, or vice versa. These alcohol dehydrogenases may also be referred to as “primary-secondary alcohol dehydrogenases”.

As discussed herein before, the invention provides a recombinant microorganism capable of producing acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of a substrate comprising CO.

In one particular embodiment, the microorganism is adapted to express one or more enzymes in the isopropanol biosynthesis pathway which are not naturally present in the parental microorganism. In another embodiment, the microorganism is adapted to over-express one or more enzymes in the isopropanol biosynthesis pathway which are naturally present in the parental microorganism.

In one particular embodiment, the microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway which are not naturally present in the parental microorganism. In another embodiment, the microorganism is adapted to over-express one or more enzymes in the acetone biosynthesis pathway which are naturally present in the parental microorganism.

In one particular embodiment, the microorganism is adapted to express one or more enzymes involved in the conversion of acetone to isopropanol which are not naturally present in the parental microorganism. In another embodiment, the microorganism is adapted to over-express one or more enzymes involved in the conversion of acetone to isopropanol which are naturally present in the parental microorganism.

In one embodiment, the parental microorganism is capable of fermenting a substrate comprising CO to produce acetone but not of converting acetone to isopropanol and the recombinant microorganism is adapted to express one or more enzymes involved in the conversion of acetone to isopropanol.

In another embodiment, the parental microorganism is capable of converting acetone to isopropanol but is not capable of fermenting a substrate comprising CO to produce acetone and the recombinant microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway.

In one embodiment, the parental microorganism is not capable of fermenting a substrate comprising CO to produce acetone and isopropanol and the recombinant microorganism is adapted to express one or more enzymes in the acetone biosynthesis pathway and one or more enzymes involved in the conversion of acetone to isopropanol.

The microorganism may be adapted to express or over-express the one or more enzymes by any number of recombinant methods including, for example, increasing expression of native genes within the microorganism (for example, by introducing a stronger or constitutive promoter to drive expression of a gene), increasing the copy number of a gene encoding a particular enzyme by introducing exogenous nucleic acids encoding and adapted to express the enzyme, introducing an exogenous nucleic acid encoding and adapted to express an enzyme not naturally present within the parental microorganism.

In certain embodiments, the parental microorganism may be transformed to provide a combination of increased or over-expression of one or more genes native to the parental microorganism and introduction of one or more genes not native to the parental microorganism. For example, one or more genes encoding an enzyme in the acetone biosynthesis pathway may be native to the parental microorganism but it may not include one or more gene encoding an enzyme involved in the conversion of acetone to isopropanol, or vice versa. The microorganism could be engineered to over-express the one or more native genes encoding an enzyme in the acetone biosynthesis pathway and to introduce a gene encoding an enzyme involved in conversion of acetone to isopropanol, or vice versa. Similarly, the microorganism could be engineered to over-express one or more enzymes in the acetone biosynthesis pathway (and/or the conversion of acetone to isopropanol) and to introduce one or more genes encoding an enzyme involved in the same pathway. Skilled persons will appreciate various other combinations of use in the invention.

In one embodiment the one or more enzymes in the acetone biosynthesis pathway are chosen from the group consisting:

Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9);

Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9);

Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9);

Acetoacetate decarboxylase (Adc; EC 4.1.1.4);

Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74); and,

A functionally equivalent variant of any one or more thereof.

By way of example only, sequence information for each of the peptides in provided in table 6 or table 18 herein after.

The enzymes used in the microorganisms of the invention may be derived from any appropriate source, including different genera and species of bacteria, or other organisms. However, in one embodiment, the Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) is that derived from C. acetobutylicum. In one embodiment, the Acetyl-Coenzyme A acetyltransferase has the amino acid sequence exemplified in table 6 herein after, or it is a functionally equivalent variant thereof.

In one embodiment, the enzymes Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) and Acetoacetate decarboxylase (Adc) are derived from C. Beijerinckii.

In one embodiment, the enzymes alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) is that derived from L. lactis.

In one embodiment, each enzyme has the amino acid sequence exemplified in table 6 or 18 herein after, or it is a functionally equivalent variant thereof.

In one embodiment, the one or more enzyme involved in the conversion of acetone to isopropanol are chosen from the group consisting:

Alcohol Dehydrogenase (Adh; EC 1.1.1.2);

Alcohol dehydrogenase (Adh2; EC 1.1.1.1); and,

A functionally equivalent variant thereof.

Again, the alcohol dehydrogenase enzyme used in the invention may be derived from any appropriate source, including different genera and species of bacteria (for example, the species of bacteria exemplified in table 13 herein after. However, in one particular embodiment, the Alcohol Dehydrogenase (Adh) is derived from C. autoethanogenum, C. ljungdahlii, and/or C. ragsdalei. In one embodiment, the alcohol dehydrogenase has the amino acid sequence of SEQ_ID NO. 1 or it is a functionally equivalent variant thereof. In one embodiment, the functionally equivalent variant has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1.

In one embodiment, the Alcohol Dehydrogenase (Adh2) is derived from S. cerevisiae.

In one embodiment, the microorganism comprises one or more exogenous nucleic acids adapted to increase expression of one or more nucleic acids native to the parental microorganism and which one or more nucleic acids encode one or more of the enzymes referred to herein before. In one embodiment, the one or more exogenous nucleic acid adapted to increase expression is a regulatory element. In one embodiment, the regulatory element is a promoter. In one embodiment, the promoter is a constitutive promoter that is preferably highly active under appropriate fermentation conditions. Inducible promoters could also be used. In preferred embodiments, the promoter is selected from the group comprising Wood-Ljungdahl gene cluster or Phosphotransacetylase/Acetate kinase operon promoters. In one embodiment, the promoter has the sequence of SEQ_ID No. 22 or 77, or is a functionally equivalent variant thereof. In another embodiment, a Wood-Ljungdahl cluster promoter (P_(WL)) (SEQ ID No. 56 or 57), the promoter region of F₁F_(o)-ATPase operon (SEQ_ID NO 51, 58 or 59), Rnf complex operon promoter region (SEQ_ID NO 52, 60 or 61), or Pyruvate:ferredoxin oxidoreductase (SEQ_ID NO 53, 62 or 63) promoter region could be used. It will be appreciated by those of skill in the art that other promoters which can direct expression, preferably a high level of expression under appropriate fermentation conditions, would be effective as alternatives to the exemplified embodiments.

In one embodiment, the microorganism comprises one or more exogenous nucleic acids encoding and adapted to express one or more of the enzymes referred to herein before. In one embodiment, the microorganisms comprise one or more exogenous nucleic acid encoding and adapted to express at least two of the enzymes. In other embodiments, the microorganism comprises one or more exogenous nucleic acid encoding and adapted to express 3, 4, 5, or 6 of the enzymes.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), and Acetoacetate decarboxylase (Adc; EC 4.1.1.4) or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exognenous nucleic acids encoding Alcohol Dehydrogenase (Adh; EC 1.1.1.2) or a functionally equivalent variant thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), and Alcohol Dehydrogenase (Adh; EC 1.1.1.2), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), and Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), or a functionally equivalent variant of any one or more thereof.

In one particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In another particular embodiment, the microorganism comprises one or more exogenous nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA; E.C. 2.3.1.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA; EC 2.8.3.9), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB; EC 2.8.3.9), Acetoacetate decarboxylase (Adc; EC 4.1.1.4), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD; EC4.1.1.74), and Alcohol dehydrogenase (Adh2; EC 1.1.1.1), or a functionally equivalent variant of any one or more thereof.

In one embodiment, Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) is encoded by a nucleic acid comprising SEQ_ID NO. 18, or a functionally equivalent variant thereof. In one embodiment, the Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) is encoded by a nucleic acid comprising SEQ_ID NO. 19, or a functionally equivalent variant thereof. In one embodiment, Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) is encoded by a nucleic acid comprising SEQ_ID NO. 20, or a functionally equivalent variant thereof. In one embodiment, Acetoacetate decarboxylase (Adc) is encoded by a nucleic acid comprising SEQ_ID NO. 21, or a functionally equivalent variant thereof. In one embodiment, the alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) is encoded by a nucleic acid comprising SEQ_ID NO. 72 or 76, or a functionally equivalent variant of any one thereof. In one embodiment, the Alcohol Dehydrogenase (Adh) is encoded by a nucleic acid comprising SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4, or a functionally equivalent variant of any one thereof. In one embodiment, the Alcohol Dehydrogenase (Adh2) is encoded by a nucleic acid comprising SEQ_ID NO. 74 or 77, or a functionally equivalent variant of any one thereof.

The microorganism may comprise one or more exogenous nucleic acids. Where it is desirable to transform the parental microorganism with two or more genetic elements (such as genes or regulatory elements (for example a promoter)) they may be contained on one or more exogenous nucleic acids.

In one embodiment, the one or more exogenous nucleic acid is a nucleic acid construct or vector, in one particular embodiment a plasmid, encoding one or more of the enzymes referred to hereinbefore in any combination. In one particular embodiment, the construct encodes each of ThlA, CtfA, CtfB, and Adc and optionally, Adh. In another embodiment, the one or more exogenous nucleic acids is a nucleic acid construct or vector, in one particular embodiment a plasmid, encoding Adh, and optionally ThlA, CtfA, CtfB, and/or Adc. In one particular embodiment, the construct encodes all of ThlA, CtfA, CtfB, Adc and Adh. The vector may also comprise other combinations of nucleic acids encoding alternative enzyme combinations, as is apparent from the description elsewhere in this document. In one particular embodiment, the vector comprises 1, 2, 3 or 4 of the nucleic acid sequences SEQ_ID NO. 19, 20, 21 and 22 or a functionally equivalent variant of any one thereof, in any order. In another embodiment, the vector comprises SEQ_ID_NO. 2, 3 and/or 4, or a functionally equivalent variant of any one thereof, in any order. In one embodiment, the vector comprises 1, 2, 3, or 4 of sequences SEQ_ID NO. 19, 20, 21 and 22 or a functionally equivalent variant of any one thereof and SEQ_ID_NO. 2, 3 or 4, or a functionally equivalent variant of any one thereof, in any order.

In another embodiment, the vector comprises one or more of SEQ ID No. 72, 76, 74, 77, alone or in combination with one or more of the nucleic acids represented by SEQ ID No. 19, 20, 21, 22, 2, 3, and 4.

The exogenous nucleic acids may remain extra-chromosomal upon transformation of the parent microorganism or may integrate into the genome of the parent microorganism. Accordingly, they may include additional nucleotide sequences adapted to assist integration (for example, a region which allows for homologous recombination and targeted integration into the host genome) or expression and replication of an extrachromosomal construct (for example, origin of replication, promoter and other regulatory elements or sequences).

In one embodiment, the exogenous nucleic acids encoding one or enzymes as mentioned herein before will further comprise a promoter adapted to promote expression of the one or more enzymes encoded by the exogenous nucleic acids. In one embodiment, the promoter is a constitutive promoter that is preferably highly active under appropriate fermentation conditions. Inducible promoters could also be used. In preferred embodiments, the promoter is selected from the group comprising Wood-Ljungdahl gene cluster and Phosphotransacetylase/Acetate kinase promoters. In one embodiment, the promoter has the sequence of SEQ_ID No. 22, SEQ ID No. 77, or is a functionally equivalent variant of any one thereof. In another embodiment, a Wood-Ljungdahl cluster promoter (P_(WL)) (SEQ ID No. 56 or 57), the promoter region of F₁F_(o)-ATPase operon (SEQ_ID NO 51, 58 or 59), Rnf complex operon promoter region (SEQ_ID NO 52, 60 or 61), or Pyruvate:ferredoxin oxidoreductase (SEQ_ID NO 53, 62 or 63) promoter region could be used. It will be appreciated by those of skill in the art that other promoters which can direct expression, preferably a high level of expression under appropriate fermentation conditions, would be effective as alternatives to the exemplified embodiments.

In one embodiment, the exogenous nucleic acid is an expression plasmid. In one particular embodiment, the expression plasmid has the nucleotide sequence SEQ_ID No. 46, 48, 83, 84, 95, 98, or 101.

In one embodiment, the parental microorganism is selected from the group of carboxydotrophic acetogenic bacteria. In certain embodiments the microorganism is selected from the group comprising Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium ragsdalei, Clostridium carboxidivorans, Clostridium drakei, Clostridium scatologenes, Clostridium coskatii, Butyribacterium limosum, Butyribacterium methylotrophicum, Acetobacterium woodii, Alkalibaculum bacchii, Blautia producta, Eubacterium limosum, Moorella thermoacetica, Moorella thermautotrophica, Oxobacter pfennigii, and Thermoanaerobacter kiuvi.

In one particular embodiment, the parental microorganism is selected from the cluster of ethanologenic, acetogenic Clostridia comprising the species C. autoethanogenum, C. ljungdahlii, and C. ragsdalei and related isolates. These include but are not limited to strains C. autoethanogenum JAI-1^(T) (DSM10061) [Abrini J, Naveau H, Nyns E-J: Clostridium autoethanogenum, sp. nov., an anaerobic bacterium that produces ethanol from carbon monoxide. Arch Microbiol 1994, 4: 345-351], C. autoethanogenum LBS1560 (DSM19630) [Simpson S D, Forster R L, Tran P T, Rowe M J, Warner I L: Novel bacteria and methods thereof. International patent 2009, WO/2009/064200], C. autoethanogenum LBS1561 (DSM23693), C. ljungdahlii PETC^(T) (DSM13528=ATCC 55383) [Tanner R S, Miller L M, Yang D: Clostridium ljungdahlii sp. nov., an Acetogenic Species in Clostridial rRNA Homology Group I. Int J Syst Bacteriol 1993, 43: 232-236], C. ljungdahlii ERI-2 (ATCC 55380) [Gaddy J L: Clostridium stain which produces acetic acid from waste gases. US patent 1997, U.S. Pat. No. 5,593,886], C. ljungdahlii C-01 (ATCC 55988) [Gaddy J L, Clausen E C, Ko C-W: Microbial process for the preparation of acetic acid as well as solvent for its extraction from the fermentation broth. US patent, 2002, U.S. Pat. No. 6,368,819], C. ljungdahlii O-52 (ATCC 55989) [Gaddy J L, Clausen E C, Ko C-W: Microbial process for the preparation of acetic acid as well as solvent for its extraction from the fermentation broth. US patent, 2002, U.S. Pat. No. 6,368,819], C. ragsdalei P11^(T) (ATCC BAA-622) [Huhnke R L, Lewis R S, Tanner R S: Isolation and Characterization of novel Clostridial Species. International patent 2008, WO 2008/028055], related isolates such as “C. coskatii” [Zahn et al—Novel ethanologenic species Clostridium coskatii (US Patent Application number US20110229947)], or mutated strains such as C. ljungdahlii OTA-1 (Tirado-Acevedo O. Production of Bioethanol from Synthesis Gas Using Clostridium ljungdahlii. PhD thesis, North Carolina State University, 2010). These strains form a subcluster within the Clostridial rRNA cluster I, and their 16S rRNA gene is more than 99% identical with a similar low GC content of around 30%. However, DNA-DNA reassociation and DNA fingerprinting experiments showed that these strains belong to distinct species [Huhnke R L, Lewis R S, Tanner R S: Isolation and Characterization of novel Clostridial Species. International patent 2008, WO 2008/028055].

All species of this cluster have a similar morphology and size (logarithmic growing cells are between 0.5-0.7×3-5 μm), are mesophilic (optimal growth temperature between 30-37° C.) and strictly anaerobe [Tanner R S, Miller L M, Yang D: Clostridium ljungdahlii sp. nov., an Acetogenic Species in Clostridial rRNA Homology Group I. Int J Syst Bacteriol 1993, 43: 232-236; Abrini J, Naveau H, Nyns E-J: Clostridium autoethanogenum, sp. nov., an anaerobic bacterium that produces ethanol from carbon monoxide. Arch Microbiol 1994, 4: 345-351; Huhnke R L, Lewis R S, Tanner R S: Isolation and Characterization of novel Clostridial Species. International patent 2008, WO 2008/028055]. Moreover, they all share the same major phylogenetic traits, such as same pH range (pH 4-7.5, with an optimal initial pH of 5.5-6), strong autotrophic growth on CO containing gases with similar growth rates, and a similar metabolic profile with ethanol and acetic acid as main fermentation end product, and small amounts of 2,3-butanediol and lactic acid formed under certain conditions. [Tanner R S, Miller L M, Yang D: Clostridium ljungdahlii sp. nov., an Acetogenic Species in Clostridial rRNA Homology Group I. Int J Syst Bacteriol 1993, 43: 232-236; Abrini J, Naveau H, Nyns E-J: Clostridium autoethanogenum, sp. nov., an anaerobic bacterium that produces ethanol from carbon monoxide. Arch Microbiol 1994, 4: 345-351; Huhnke R L, Lewis R S, Tanner R S: Isolation and Characterization of novel Clostridial Species. International patent 2008, WO 2008/028055]. Indole production was observed with all three species as well. However, the species differentiate in substrate utilization of various sugars (e.g. rhamnose, arabinose), acids (e.g. gluconate, citrate), amino acids (e.g. arginine, histidine), or other substrates (e.g. betaine, butanol). Moreover some of the species were found to be auxotroph to certain vitamins (e.g. thiamine, biotin) while others were not.

In one embodiment, the parental strain uses CO as its sole carbon and energy source.

In one embodiment the parental microorganism is Clostridium autoethanogenum or Clostridium ljungdahlii. In one particular embodiment, the microorganism is Clostridium autoethanogenum DSM23693. In another particular embodiment, the microorganism is Clostridium ljungdahlii DSM13528 (or ATCC55383).

In one embodiment, the parental microorganism lacks one or more genes encoding ThlA, CtfA, CtfB, Adc, KivD, Adh and Adh2. In one particular embodiment, the parental microorganism lacks a gene encoding Adh. In another particular embodiment, the parental microorganism lacks each of the genes encoding ThlA, CtfA, CtfB, Adc, and KivD.

The inventors have identified a novel Adh protein. Accordingly, the invention provides an Alcohol Dehydrogenase (Adh) having the amino acid sequence of SEQ_ID NO. 1, or a functionally equivalent variant of any one thereof. In one particular embodiment, the functionally equivalent variant of Alcohol Dehydrogenase (Adh) has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1.

In addition the invention provides a nucleic acid encoding Adh of SEQ_ID NO. 1 or a functionally equivalent variant thereof. Skilled persons will readily appreciate such nucleic acids, having regard to the amino acid sequence provided herein and the genetic code and the degeneracy therein. However, by way of example, nucleic acids encoding Adh of SEQ_ID NO. 1 include the nucleic acids of SEQ_ID NO. 2, 3 or 4, or functionally equivalent variants thereof. In one particular embodiment, a functionally equivalent variant of SEQ_ID NO. 2, 3 or 4 is a nucleic acid having at least approximately 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 2, 3 or 4.

The invention also provides nucleic acids which are capable of hybridising to at least a portion of the nucleic acid SEQ_ID NO. 2, 3 or 4, a nucleic acid complementary to any one thereof, or a functionally equivalent variant of any one thereof. Such nucleic acids will preferably hybridise to the nucleic acid of SEQ_ID NO. 2, 3 or 4, a nucleic acid complementary to any one thereof, or a functionally equivalent variant of any one thereof, under stringent hybridisation conditions. “Stringent hybridisation conditions” means that the nucleic acid is capable of hybridising to a target template under standard hybridisation conditions such as those described in Sambrook et al, Molecular Cloning: A Laboratory Manual (1989), Cold Spring Harbor Laboratory Press, New York, USA. It will be appreciated that the minimal size of such nucleic acids is a size which is capable of forming a stable hybrid between a given nucleic acid and the complementary sequence to which it is designed to hybridise. Accordingly, the size is dependent on the nucleic acid composition and percent homology between the nucleic acid and its complementary sequence, as well as the hybridisation conditions which are utilised (for example, temperature and salt concentrations). In one embodiment, the nucleic acid is at least 10 nucleotides in length, at least 15 nucleotides in length, at least, 20 nucleotides in length, at least 25 nucleotides in length, or at least 30 nucleotides in length.

The inventor's have also identified a number of novel nucleic acids useful as probes and primers, as detailed herein after in the examples section. For example, SEQ_ID NO. 5; SEQ_ID NO. 6; SEQ_ID NO. 7; SEQ_ID NO. 8; SEQ_ID NO. 9; SEQ_ID NO. 10; SEQ_ID NO. 11; SEQ_ID NO. 12; SEQ_ID NO. 13; SEQ_ID NO. 14; SEQ_ID NO. 15; SEQ_ID NO. 16; SEQ_ID NO. 17; SEQ_ID NO. 18; SEQ_ID NO. 23; SEQ_ID NO. 24; SEQ_ID NO. 25; SEQ_ID NO. 26; SEQ_ID NO. 27; SEQ_ID NO. 28; SEQ_ID NO. 29; SEQ_ID NO. 30; SEQ_ID NO. 31; SEQ_ID NO. 32; SEQ_ID NO. 33; SEQ_ID NO. 64; SEQ_ID NO. 65; SEQ_ID NO. 66; SEQ_ID NO. 67; SEQ_ID NO. 68; SEQ_ID NO. 69; SEQ_ID NO. 70; SEQ_ID NO. 71; SEQ_ID NO. 85; SEQ_ID NO. 86; SEQ_ID NO. 87; SEQ_ID NO. 88; SEQ_ID NO. 89; SEQ_ID NO. 90; SEQ_ID NO. 91; SEQ_ID NO. 92; SEQ_ID NO. 93; SEQ_ID NO. 94; SEQ_ID NO. 96; SEQ_ID NO. 97; SEQ_ID NO. 99; SEQ_ID NO. 100.

The invention also provides nucleic acids and nucleic acid constructs of use in generating a recombinant microorganism of the invention.

In one embodiment, the nucleic acids comprises sequences encoding one or more of the enzymes which when expressed in a microorganism allows the microorganism to produce acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of substrate comprising CO. In one particular embodiment, the invention provides a nucleic acid encoding two or more enzymes which when expressed in a microorganism allows the microorganism to produce acetone, isopropanol and/or a precursor of acetone and/or isopropanol by fermentation of substrate comprising CO. In one embodiment, the nucleic acids of the invention encode 3, 4, 5 or 6 such enzymes.

In one particular embodiment, the enzymes are chosen from Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), ketoisovalerate decarboxylase (decarboxylase; KivD), Alcohol Dehydrogenase (Adh), Alcohol Dehydrogenase (Adh2), and a functionally equivalent variant of any one or more thereof.

In one embodiment, a nucleic acid of the invention comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), and Acetoacetate decarboxylase (Adc) or a functionally equivalent variant of any one or more thereof, in any order

In one embodiment, a nucleic acid of the invention comprises nucleic acid sequences encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), and Alcohol Dehydrogenase (Adh) or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, a nucleic acid of the invention comprises nucleic acid sequences encoding each of Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), and Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, a nucleic acid of the invention comprises nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), and Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), or a functionally equivalent variant of any one or more thereof, in any order.

In one embodiment, a nucleic acid of the invention comprises nucleic acids encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), or a functionally equivalent variant thereof.

In one one embodiment, a nucleic acid of the invention comprises nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), and Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

In another embodiment, a nucleic acid of the invention comprises nucleic acids encoding each of Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA), Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase), Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB), Acetoacetate decarboxylase (Adc), Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD), and Alcohol dehydrogenase (Adh2), or a functionally equivalent variant of any one or more thereof, in any order.

Exemplary amino acid sequences and nucleic acid sequence encoding each of the above enzymes are provided in GenBank as described elsewhere herein (see, in particular, the examples provided in tables 6 and 18 herein after). However, skilled persons will readily appreciate alternative nucleic acids sequences encoding the enzymes or functionally equivalent variants thereof, having regard to the information contained herein, in GenBank and other databases, and the genetic code.

In one embodiment, Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) has the sequence of Seq_ID No. 42 or a functionally equivalent variant thereof. In one embodiment, the Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) has the sequence of Seq_ID No. 43, or a functionally equivalent variant thereof. In one embodiment, Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) has the sequence of Seq_ID No. 44 or a functionally equivalent variant thereof. In one embodiment, Acetoacetate decarboxylase (Adc) has the sequence of Seq_ID No. 45, or a functionally equivalent variant thereof. In one embodiment, Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) has the sequence of Seq_ID No. 73, or a functionally equivalent variant thereof. In one embodiment, Alcohol Dehydrogenase (Adh) has the sequence of SEQ_ID NO 38 and SEQ_ID NO 40. In one particular embodiment, the Alcohol Dehydrogenase (Adh) has the sequence of SEQ_ID NO. 1, or a functionally equivalent variant thereof. In one particular embodiment, the functionally equivalent variant of Alcohol Dehydrogenase (Adh) has at least approximately 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 1. In one embodiment, Alcohol Dehydrogenase (Adh2) has the sequence of SEQ_ID NO 75, or a functionally equivalent variant thereof.

In one embodiment, the nucleic acid sequence encoding Acetyl-Coenzyme A acetyltransferase (Thiolase; ThlA) comprises SEQ_ID NO. 18, or is a functionally equivalent variant thereof. In one embodiment, the nucleic acid sequence encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase A (CoA transferase; CtfA) comprises SEQ_ID NO. 19, or is a functionally equivalent variant thereof. In one embodiment, the nucleic acid sequence encoding Acetoacetyl-CoA:Acetate Coenzyme A transferase B (CoA transferase; CtfB) comprises SEQ_ID NO. 20, or is a functionally equivalent variant thereof. In one embodiment, the nucleic acid sequence encoding Acetoacetate decarboxylase (Adc) comprises SEQ_ID NO. 21, or is a functionally equivalent variant thereof. In one embodiment, the nucleic acid sequence encoding Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) comprises SEQ_ID NO. 72 or 76, or is a functionally equivalent variant of any one thereof. In one embodiment, the nucleic acid sequence encoding Alcohol Dehydrogenase (Adh2) comprises SEQ_ID NO. 74 or 77, or is a functionally equivalent variant thereof. In one embodiment, the nucleic acid sequence encoding Alcohol Dehydrogenase (Adh) comprises Seq_ID No. 39 or SEQ_ID NO 41, or is a functionally equivalent variant of any one thereof. In one particular embodiment, the nucleic acid sequence encoding Alcohol Dehydrogenase (Adh) comprises SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4, or is a functionally equivalent variant of any one thereof. In one embodiment, the functionally equivalent variant of SEQ_ID NO. 2, SEQ_ID NO. 3, or SEQ_ID NO. 4 has at least approximately 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% sequence identity to SEQ_ID NO. 2, 3 or 4.

In one embodiment, the nucleic acids of the invention will further comprise a promoter. In one embodiment, the promoter allows for constitutive expression of the genes under its control. However, inducible promoters may also be employed. Persons of skill in the art will readily appreciate promoters of use in the invention. Preferably, the promoter can direct a high level of expression under appropriate fermentation conditions. In a particular embodiment a Wood-Ljungdahl cluster promoter is used. In another embodiment, a Phosphotransacetylase/Acetate kindase promoter is used. In another embodiment a pyruvate:ferredoxin oxidoreductase promoter, an Rnf complex operon promoter or an ATP synthase operon promoter. In one particular embodiment, the promoter is from C. autoethanogenum. In one particular embodiment, the promoter has the sequence of SEQ_ID NO. 22, SEQ ID No 79, or is a functionally equivalent variant of any one thereof. In other embodiments, the promoter has the sequence of SEQ ID No. 56, 57, 51, 58, 59, 52, 60, 61, 53, 62 or 63, or is a functionally equivalent variant of any one thereof.

The nucleic acids of the invention may remain extra-chromosomal upon transformation of a parental microorganism or may be adapted for intergration into the genome of the microorganism. Accordingly, nucleic acids of the invention may include additional nucleotide sequences adapted to assist integration (for example, a region which allows for homologous recombination and targeted integration into the host genome) or stable expression and replication of an extrachromosomal construct (for example, origin of replication, promoter and other regulatory sequences).

In one embodiment, the nucleic acid is nucleic acid construct or vector. In one particular embodiment, the nucleic acid construct or vector is an expression construct or vector, however other constructs and vectors, such as those used for cloning are encompassed by the invention. In one particular embodiment, the expression construct or vector is a plasmid. In one particular embodiment, the expression plasmid has the nucleotide sequence SEQ_ID No. 46, 48, 83, 84, 95, 98 or 101.

It will be appreciated that an expression construct/vector of the present invention may contain any number of regulatory elements in addition to the promoter as well as additional genes suitable for expression of further proteins if desired. In one embodiment the expression construct/vector includes one promoter. In another embodiment, the expression construct/vector includes two or more promoters. In one particular embodiment, the expression construct/vector includes one promoter for each gene to be expressed. In one embodiment, the expression construct/vector includes one or more ribosomal binding sites, preferably a ribosomal binding site for each gene to be expressed.

It will be appreciated by those of skill in the art that the nucleic acid sequences and construct/vector sequences described herein may contain standard linker nucleotides such as those required for ribosome binding sites and/or restriction sites. Such linker sequences should not be interpreted as being required and do not provide a limitation on the sequences defined.

Nucleic acids and nucleic acid constructs, including expression constructs/vectors of the invention may be constructed using any number of techniques standard in the art. For example, chemical synthesis or recombinant techniques may be used. Such techniques are described, for example, in Sambrook et al (Molecular Cloning: A laboratory manual, Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., 1989). Further exemplary techniques are described in the Examples section herein after. Essentially, the individual genes and regulatory elements will be operably linked to one another such that the genes can be expressed to form the desired proteins. Suitable vectors for use in the invention will be appreciated by those of ordinary skill in the art. However, by way of example, the following vectors may be suitable: pMTL80000 vectors, pIMP1, pJIR750, and the plasmids exemplified in the Examples section herein after.

It should be appreciated that nucleic acids of the invention may be in any appropriate form, including RNA, DNA, or cDNA.

The invention also provides host organisms, particularly microorganisms, and including viruses, bacteria, and yeast, comprising any one or more of the nucleic acids described herein.

The one or more exogenous nucleic acids may be delivered to a parental microorganism as naked nucleic acids or may be formulated with one or more agents to facilitate the transformation process (for example, liposome-conjugated nucleic acid, an organism in which the nucleic acid is contained). The one or more nucleic acids may be DNA, RNA, or combinations thereof, as is appropriate. Restriction inhibitors may be used in certain embodiments; see, for example Murray, N. E. et al. (2000) Microbial. Molec. Biol. Rev. 64, 412.)

The microorganisms of the invention may be prepared from a parental microorganism and one or more exogenous nucleic acids using any number of techniques known in the art for producing recombinant microorganisms. By way of example only, transformation (including transduction or transfection) may be achieved by electroporation, ultrasonication, polyethylene glycol-mediated transformation, chemical or natural competence, or conjugation. Suitable transformation techniques are described for example in, Sambrook J, Fritsch E F, Maniatis T: Molecular Cloning: A laboratory Manual, Cold Spring Harbour Laboratory Press, Cold Spring Harbour, 1989.

In certain embodiments, due to the restriction systems which are active in the microorganism to be transformed, it is necessary to methylate the nucleic acid to be introduced into the microorganism. This can be done using a variety of techniques, including those described below, and further exemplified in the Examples section herein after.

By way of example, in one embodiment, a recombinant microorganism of the invention is produced by a method comprises the following steps:

introduction into a shuttle microorganism of (i) of an expression construct/vector as described herein and (ii) a methylation construct/vector comprising a methyltransferase gene;

expression of the methyltransferase gene;

isolation of one or more constructs/vectors from the shuttle microorganism; and,

introduction of the one or more construct/vector into a destination microorganism.

In one embodiment, the methyltransferase gene of step B is expressed constitutively. In another embodiment, expression of the methyltransferase gene of step B is induced.

The shuttle microorganism is a microorganism, preferably a restriction negative microorganism, that facilitates the methylation of the nucleic acid sequences that make up the expression construct/vector. In a particular embodiment, the shuttle microorganism is a restriction negative E. coli, Bacillus subtillis, or Lactococcus lactis.

The methylation construct/vector comprises a nucleic acid sequence encoding a methyltransferase.

Once the expression construct/vector and the methylation construct/vector are introduced into the shuttle microorganism, the methyltransferase gene present on the methylation construct/vector is induced. Induction may be by any suitable promoter system although in one particular embodiment of the invention, the methylation construct/vector comprises an inducible lac promoter (preferably encoded by SEQ_ID NO 50) and is induced by addition of lactose or an analogue thereof, more preferably isopropyl-β-D-thio-galactoside (IPTG). Other suitable promoters include the ara, tet, or T7 system. In a further embodiment of the invention, the methylation construct/vector promoter is a constitutive promoter.

In a particular embodiment, the methylation construct/vector has an origin of replication specific to the identity of the shuttle microorganism so that any genes present on the methylation construct/vector are expressed in the shuttle microorganism. Preferably, the expression construct/vector has an origin of replication specific to the identity of the destination microorganism so that any genes present on the expression construct/vector are expressed in the destination microorganism.

Expression of the methyltransferase enzyme results in methylation of the genes present on the expression construct/vector. The expression construct/vector may then be isolated from the shuttle microorganism according to any one of a number of known methods. By way of example only, the methodology described in the Examples section described hereinafter may be used to isolate the expression construct/vector.

In one particular embodiment, both construct/vector are concurrently isolated.

The expression construct/vector may be introduced into the destination microorganism using any number of known methods. However, by way of example, the methodology described in the Examples section hereinafter may be used. Since the expression construct/vector is methylated, the nucleic acid sequences present on the expression construct/vector are able to be incorporated into the destination microorganism and successfully expressed.

It is envisaged that a methyltransferase gene may be introduced into a shuttle microorganism and over-expressed. Thus, in one embodiment, the resulting methyltransferase enzyme may be collected using known methods and used in vitro to methylate an expression plasmid. The expression construct/vector may then be introduced into the destination microorganism for expression. In another embodiment, the methyltransferase gene is introduced into the genome of the shuttle microorganism followed by introduction of the expression construct/vector into the shuttle microorganism, isolation of one or more constructs/vectors from the shuttle microorganism and then introduction of the expression construct/vector into the destination microorganism.

It is envisaged that the expression construct/vector and the methylation construct/vector as defined above may be combined to provide a composition of matter. Such a composition has particular utility in circumventing restriction barrier mechanisms to produce the recombinant microorganisms of the invention.

In one particular embodiment, the expression construct/vector and/or the methylation construct/vector are plasmids.

Persons of ordinary skill in the art will appreciate a number of suitable methyltransferases of use in producing the microorganisms of the invention. However, by way of example the Bacillus subtilis phage ΦT1 methyltransferase and the methyltransferase described in the Examples herein after may be used. In one embodiment, the methyltransferase has the amino acid sequence of SEQ_ID No. 34, or is a functionally equivalent variant thereof. Nucleic acids encoding suitable methyltransferases will be readily appreciated having regard to the sequence of the desired methyltransferase and the genetic code. In one embodiment, the nucleic acid encoding a methyltransferase is as described in the Examples herein after (for example the nucleic acid of SEQ_ID NO 35, or it is a functionally equivalent variant thereof).

Any number of constructs/vectors adapted to allow expression of a methyltransferase gene may be used to generate the methylation construct/vector. However, by way of example, the plasmid described in the Examples section hereinafter may be used. In one particular embodiment, the plasmid has the sequence of SEQ_ID NO. 49.

The invention provides a method for the production of one or more desirable products (acetone, isopropanol, and/or or a precursor of acetone and/or isopropanol) by microbial fermentation comprising fermenting a substrate comprising CO using a recombinant microorganism of the invention. The methods of the invention may be used to reduce the total atmospheric carbon emissions from an industrial process.

Preferably, the fermentation comprises the steps of anaerobically fermenting a substrate in a bioreactor to produce the one or more products using a recombinant microorganism of the invention.

In one embodiment the method comprises the steps of:

-   -   (a) providing a substrate comprising CO to a bioreactor         containing a culture of one or more microorganism of the         invention; and     -   (b) anaerobically fermenting the culture in the bioreactor to         produce the one or more products.

In one embodiment the method comprises the steps of:

-   -   (a) capturing CO-containing gas produced as a result of the         industrial process, before the gas is released into the         atmosphere;     -   (b) the anaerobic fermentation of the CO-containing gas to         produce the one or more products by a culture containing one or         more microorganism of the invention.

In an embodiment of the invention, the gaseous substrate fermented by the microorganism is a gaseous substrate containing CO. The gaseous substrate may be a CO-containing waste gas obtained as a by-product of an industrial process, or from some other source such as from automobile exhaust fumes. In certain embodiments, the industrial process is selected from the group consisting of ferrous metal products manufacturing, such as a steel mill, non-ferrous products manufacturing, petroleum refining processes, gasification of coal, electric power production, carbon black production, ammonia production, methanol production and coke manufacturing. In these embodiments, the CO-containing gas may be captured from the industrial process before it is emitted into the atmosphere, using any convenient method. The CO may be a component of syngas (gas comprising carbon monoxide and hydrogen). The CO produced from industrial processes is normally flared off to produce CO₂ and therefore the invention has particular utility in reducing CO₂ greenhouse gas emissions and producing butanol for use as a biofuel. Depending on the composition of the gaseous CO-containing substrate, it may also be desirable to treat it to remove any undesired impurities, such as dust particles before introducing it to the fermentation. For example, the gaseous substrate may be filtered or scrubbed using known methods.

It will be appreciated that for growth of the bacteria and CO-to-the one or more product(s) to occur, in addition to the CO-containing substrate gas, a suitable liquid nutrient medium will need to be fed to the bioreactor. The substrate and media may be fed to the bioreactor in a continuous, batch or batch fed fashion. A nutrient medium will contain vitamins and minerals sufficient to permit growth of the micro-organism used. Anaerobic media suitable for fermentation to produce butanol using CO are known in the art. For example, suitable media are described Biebel (2001). In one embodiment of the invention the media is as described in the Examples section herein after.

The fermentation should desirably be carried out under appropriate conditions for the CO-to-the one or more product(s) fermentation to occur. Reaction conditions that should be considered include pressure, temperature, gas flow rate, liquid flow rate, media pH, media redox potential, agitation rate (if using a continuous stirred tank reactor), inoculum level, maximum gas substrate concentrations to ensure that CO in the liquid phase does not become limiting, and maximum product concentrations to avoid product inhibition.

In addition, it is often desirable to increase the CO concentration of a substrate stream (or CO partial pressure in a gaseous substrate) and thus increase the efficiency of fermentation reactions where CO is a substrate. Operating at increased pressures allows a significant increase in the rate of CO transfer from the gas phase to the liquid phase where it can be taken up by the micro-organism as a carbon source for the production of the one or more products. This in turn means that the retention time (defined as the liquid volume in the bioreactor divided by the input gas flow rate) can be reduced when bioreactors are maintained at elevated pressure rather than atmospheric pressure. The optimum reaction conditions will depend partly on the particular micro-organism of the invention used. However, in general, it is preferred that the fermentation be performed at pressure higher than ambient pressure. Also, since a given CO-to-the one or more product(s) conversion rate is in part a function of the substrate retention time, and achieving a desired retention time in turn dictates the required volume of a bioreactor, the use of pressurized systems can greatly reduce the volume of the bioreactor required, and consequently the capital cost of the fermentation equipment. According to examples given in U.S. Pat. No. 5,593,886, reactor volume can be reduced in linear proportion to increases in reactor operating pressure, i.e. bioreactors operated at 10 atmospheres of pressure need only be one tenth the volume of those operated at 1 atmosphere of pressure.

By way of example, the benefits of conducting a gas-to-ethanol fermentation at elevated pressures has been described. For example, WO 02/08438 describes gas-to-ethanol fermentations performed under pressures of 30 psig and 75 psig, giving ethanol productivities of 150 g/l/day and 369 g/l/day respectively. However, example fermentations performed using similar media and input gas compositions at atmospheric pressure were found to produce between 10 and 20 times less ethanol per litre per day.

It is also desirable that the rate of introduction of the CO-containing gaseous substrate is such as to ensure that the concentration of CO in the liquid phase does not become limiting. This is because a consequence of CO-limited conditions may be that the ethanol product is consumed by the culture.

The composition of gas streams used to feed a fermentation reaction can have a significant impact on the efficiency and/or costs of that reaction. For example, O2 may reduce the efficiency of an anaerobic fermentation process. Processing of unwanted or unnecessary gases in stages of a fermentation process before or after fermentation can increase the burden on such stages (e.g. where the gas stream is compressed before entering a bioreactor, unnecessary energy may be used to compress gases that are not needed in the fermentation). Accordingly, it may be desirable to treat substrate streams, particularly substrate streams derived from industrial sources, to remove unwanted components and increase the concentration of desirable components.

In certain embodiments a culture of a bacterium of the invention is maintained in an aqueous culture medium. Preferably the aqueous culture medium is a minimal anaerobic microbial growth medium. Suitable media are known in the art and described for example in U.S. Pat. Nos. 5,173,429 and 5,593,886 and WO 02/08438, and as described in the Examples section herein after.

Acetone, isopropanol, or a mixed stream containing acetone and/or isopropanol and/or one or more other products, may be recovered from the fermentation broth by methods known in the art, such as fractional distillation or evaporation, pervaporation, gas stripping and extractive fermentation, including for example, liquid-liquid extraction.

In certain preferred embodiments of the invention, the one or more products are recovered from the fermentation broth by continuously removing a portion of the broth from the bioreactor, separating microbial cells from the broth (conveniently by filtration), and recovering one or more products from the broth. Alcohols may conveniently be recovered for example by distillation. Acetone may be recovered for example by distillation. Any acids produced may be recovered for example by adsorption on activated charcoal. The separated microbial cells are preferably returned to the fermentation bioreactor. The cell free permeate remaining after any alcohol(s) and acid(s) have been removed is also preferably returned to the fermentation bioreactor. Additional nutrients (such as B vitamins) may be added to the cell free permeate to replenish the nutrient medium before it is returned to the bioreactor.

Also, if the pH of the broth was adjusted as described above to enhance adsorption of acetic acid to the activated charcoal, the pH should be re-adjusted to a similar pH to that of the broth in the fermentation bioreactor, before being returned to the bioreactor.

Examples

The invention will now be described in more detail with reference to the following non-limiting examples.

Microorganisms and Growth Conditions

Acetobacterium woodii DSM1030, Clostridium aceticum DSM1496, C. autoethanogenum DSM23693, C. carboxidivorans DSM15243, and C. ljungdahlii DSM13528 were sourced from DSMZ (The German Collection of Microorganisms and Cell Cultures, Inhoffenstraβe 7 B, 38124 Braunschweig, Germany). C. autoethanogenum DSM23693 is a derivate of C. autoethanogenum DSM10061.

C. ragsdalei ATCC BAA-622 were sourced from the American Type Culture Collection, Manassas, Va. 20108, USA.

C. acetobutylicum ATCC824, C. beijerinckii NRRL-B593, and C. beijerinckii NCIMB8052 were obtained from Prof. David Jones (University of Otago) and can also be obtained from public strain collections DSMZ and ATCC under accession numbers ATCC824/DSM792, DSM6423, and ATCC51743 respectively.

Escherichia coli DH5α-T1^(R) was sourced from Invitrogen, Carlsbad, Calif. 92008, USA and Escherichia coli XL1-Blue MRF′ Kan and ABLE K from Stratagene (Santa Clara, Calif. 95051-7201, USA). Escherichia coli JW3350-2 was sourced from The Coli Genetic Stock Center (CGSC), New Haven, Conn. 06520-8103.

E. coli was cultivated under both aerobic and anaerobic conditions, while all other strains were grown strictly anaerobically in a volume of 50 ml liquid media in serum bottles with fructose (heterotrophic growth) or 30 psi CO-containing steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ; composition: 44% CO, 32% N₂, 22% CO₂, 2% H₂) in the headspace (autotrophic growth).

Media was prepared using standard anaerobic techniques [Hungate R E: A roll tube method for cultivation of strict anaerobes, in Norris J R and Ribbons D W (eds.), Methods in Microbiology, vol. 3B. Academic Press, New York, 1969: 117-132; Wolfe R S: Microbial formation of methane. Adv Microb Physiol 1971, 6: 107-146] according to formulations are given in Tab. 2-4. For solid media, 1.2% Bacto agar (BD, Frankton Lakes, N.J. 07417, USA) was added.

All strains were grown at 37° C., except for A. woodii, C. aceticum, and C. ragsdalei which were grown at 30° C.

TABLE 2 PETC medium (A. woodii, pH 8.2; C. aceticum, pH 7.4; C. autoethanogenum, C. carboxidivorans, C. ljungdahlii, and C. ragsdalei, pH 5.6) Media component Concentration per 1.0 L of media NH₄Cl 1 g KCl 0.1 g MgSO₄•7H₂O 0.2 g NaCl 0.8 g KH₂PO₄ 0.1 g CaCl₂ 0.02 g Trace metal solution (see below) 10 ml Wolfe's vitamin solution (see below) 10 ml Yeast Extract (optional) 1 g Resazurin (2 g/L stock) 0.5 ml NaHCO₃ 2 g Reducing agent 0.006-0.008% (v/v) Fructose (for heterotrophic growth) 5 g Trace metal solution per L of stock Nitrilotriacetic Acid 2 g MnSO₄•H₂O 1 g Fe(SO₄)₂(NH₄)₂•6H₂O 0.8 g CoCl₂•6H₂O 0.2 g ZnSO₄•7H₂O 0.2 mg CuCl₂•2H₂O 0.02 g NaMoO₄•2H₂O 0.02 g Na₂SeO₃ 0.02 g NiCl₂•6H₂O 0.02 g Na₂WO₄•2H₂O 0.02 g Reducing agent stock per 100 ml of stock NaOH 0.9 g   Cystein•HCl 4 g Na₂S 4 g

TABLE 3 Reinforced Clostridial Medium RCM (C. acetobutylicum, C. beijerinckii) Media component Concentration per 1.0 L of media Pancreatic Digest of Casein 5 g Proteose Peptone No. 3 5 g Beef Extract 10 g  Yeast Extract 3 g Dextrose 5 g NaCl 5 g Soluble starch 1 g Cystein•HCl 0.5 g   Sodium Acetate 3 g

TABLE 4 Luria Bertani medium LB (E. coli) Media component Concentration per 1.0 L of media Tryptone 10 g Yeast Extract  5 g NaCl 10 g

TABLE 5 SD-8 minimal media (E. coli) Media component Concentration per 1.0 L of media NH₄Cl 7 g Na₂HPO₄ 7.5 g K₂SO₄ 0.85 g MgSO₄•7H₂O 0.17 g KH₂PO₄ 7.5 g Trace metal solution (see below) 0.8 ml Yeast Extract 5 g Glucose 2 0 g Trace metal solution per 100 L of stock MnSO₄•H₂O   1 g FeSO₄•7H₂O   4 g CoCl₂•6H₂O 0.4 g ZnSO₄•7H₂O 0.2 g CuCl₂•2H₂O 0.1 g Na₂MoO₄•2H₂O 0.2 g Al₂(SO₄)₃ 2.83 g  H₃BO₄ 0.5 g

Fermentations with C. autoethanogenum DSM23693 were carried out in 1.5 L bioreactors at 37° C. and CO-containing steel mill gas as sole energy and carbon source as described below. A defined medium was used containing per litre: MgCl, CaCl₂ (0.5 mM), KCl (2 mM), H₃PO₄ (5 mM), Fe (100 μM), Ni, Zn (5 μM), Mn, B, W, Mo, Se(2 μM) was prepared for culture growth. The media was transferred into the bioreactor and autoclaved at 121° C. for 45 minutes. After autoclaving, the medium was supplemented with Thiamine, Pantothenate (0.05 mg), Biotin (0.02 mg) and reduced with 3 mM Cysteine-HCl. To achieve anaerobicity the reactor vessel was sparged with nitrogen through a 0.2 μm filter. Prior to inoculation, the gas was switched to CO-containing steel mill gas, feeding continuously to the reactor. The gas flow was initially set at 80 ml/min, increasing to 200 ml/min during mid exponential phase, while the agitation was increased from 200 rpm to 350. Na₂S was dosed into the bioreactor at 0.25 ml/hr. Once the OD600 reached 0.5, the bioreactor was switched to a continuous mode at a rate of 1.0 ml/min (Dilution rate 0.96 d⁻¹). Media samples were taken to measure the biomass and metabolites and a headspace analysis of the in- and outflowing gas was performed on regular basis.

Analysis of Metabolites

HPLC analysis of acetone, isopropanol and other metabolites was performed using an Agilent 1100 Series HPLC system equipped with a RID operated at 35° C. (Refractive Index Detector) and an Alltech IOA-2000 Organic acid column (150×6.5 mm, particle size 5 μm) kept at 60° C. Slightly acidified water was used (0.005 M H₂SO₄) as mobile phase with a flow rate of 0.7 ml/min. To remove proteins and other cell residues, 400 μl samples were mixed with 100 μl of a 2% (w/v) 5-Sulfosalicylic acid and centrifuged at 14,000×g for 3 min to separate precipitated residues. 10 μl of the supernatant were then injected into the HPLC for analyses.

GC analysis of acetone, isopropanol and other metabolites was performed using an Agilent 6890N headspace GC equipped with a Supelco PDMS 100 1 cm fiber, an Alltech EC-1000 (30 m×0.25 mm×0.25 μm) column, and a flame ionization detector (FID). 5 ml samples were transferred into a Hungate tube, heated to 40° C. in a water bath and exposed to the fiber for exactly 5 min. The injector was kept at 250° C. and helium with a constant flow of 1 ml/min was used as carrier gas. The oven program was 40° C. for 5 min, followed by an increase of 10° C./min up to 200° C. The temperature was then further increased to 220° C. with a rate of 50° C./min followed by a 5 min hold this temperature, before the temperature was decreased to 40° C. with a rate of 50° C./min and a final 1 min hold. The FID was kept at 250° C. with 40 ml/min hydrogen, 450 ml/min air and 15 ml/min nitrogen as make up gas.

Headspace Analysis

Measurements were carried out on a Varian CP-4900 micro GC with two installed channels. Channel 1 was a 10 m Mol-sieve column running at 70° C., 200 kPa argon and a backflush time of 4.2 s, while channel 2 was a 10 m PPQ column running at 90° C., 150 kPa helium and no backflush. The injector temperature for both channels was 70° C. Runtimes were set to 120 s, but all peaks of interest would usually elute before 100 s.

Genetic Modification of C. autoethanogenum and C. ljungdahlii for Acetone Production Using Clostridial Pathway

C. autoethanogenum and C. ljungdahlii are naturally not able to produce acetone, therefore the acetone biosynthesis pathway occurring in other Clostridial species was introduced into both organisms (FIG. 4). The first step in the Clostridial acetone biosynthesis pathway from acetyl-CoA to acetoacetyl-CoA is catalysed by a acetyl-Coenzyme A acetyltransferase or thiolase. The conversion of acetoacetyl-CoA to acetone is then catalysed by a specialized set of enzymes acetate/butyrate-acetoacetate CoA-transferase complex and acetoacetate decarboxylase, which can be found in few organisms like C. acetobutylicum and C. beijerinckii (Tab. 6).

TABLE 6 Accession numbers of genes and enzymes involved in acetone and isopropanol formation. C. acetobutylicum C. beijerinckii Description nucleic acid amino acid nucleic acid Amino acid Thiolase (ThlA) NC_003030.1; NP_349476.1 NC_009617; YP_001310706.1 GI: 1119056 GI: 5294796 Acetate/Butyrate-acetoacetate NC_001988.2; NP_149326.1 NC_009617; YP_001310904.1 CoA-transferase subunit A (CtfA) GI: 1116168 GI: 5294994 Acetate/Butyrate-acetoacetate NC_001988.2; NP_149327.1 NC_009617; YP_001310905.1 CoA-transferase subunit A CtfB GI: 1116169 GI: 5294995 Acetoacetate decarboxylase NC_001988.2; NP_149328.1 NC_009617; YP_001310906.1 (Adc) GI: 1116170 GI: 5294996

Whereas the genes of C. acetobutylicum encoding the respective enzymes are split into 2 operons, the genes of C. beijerinckii form a common operon, which the inventor(s) believe offers an advantage. The genes encoding a thiolase from C. acetobutylicum and the operon coding for enzymes acetate/butyrate-acetoacetate CoA-transferase subunit A, acetate/butyrate-acetoacetate CoA-transferase subunit B and acetoacetate decarboxylase were assembled into a synthetic operon under control of a strong, native C. autoethanogenum promoter (FIG. 3). This construct was used to genetically engineer both organism for acetone production. In order to create a recombinant strain, a novel methyltransferase was used to methylate the construct, which was then transformed and expressed in C. autoethanogenum DSM23693 and C. ljungdahlii DSM13528 (described herein after). Production of acetone was shown on different industrial gas streams (steel mill waste gas, syngas).

Construction of Expression Plasmid with Clostridial Acetone Pathway Genes:

Standard Recombinant DNA and molecular cloning techniques were used in this invention [Sambrook J, Fritsch E F, Maniatis T: Molecular Cloning: A laboratory Manual, Cold Spring Harbour Laboratory Press, Cold Spring Harbour, 1989; Ausubel F M, Brent R, Kingston R E, Moore D D, Seidman J G, Smith J A, Struhl K: Current protocols in molecular biology. John Wiley & Sons, Ltd., Hoboken, 1987]. DNA sequences of acetone biosynthetic genes are shown in Tab. 7. The Wood-Ljungdahl cluster promoter of C. autoethanogenum (upstream of CO dehydrogenase gene acsA) was used for expression of target genes (Tab. 7).

TABLE 7 Sequences used for Clostridial acetone expression plasmid SEQ_ID Description Source NO. Thiolase (thlA) Clostridium acetobutylicum ATCC 824; 18 NC_003030.1; GI: 1119056 Acetoacetyl-CoA:acetate Clostridium beijerinckii NCIMB 8052; 47 Coenzyme A transferase A NC_009617; region: 4,400,524-4,402,656; (ctfA), acetoacetyl-CoA:acetate including GI: 5294994, GI: 5294995, and GI: Coenzyme A transferase B (ctfB), 5294996 and acetoacetate decarboxylase (adc) operon Wood-Ljungdahl cluster Clostridium autoethanogenum DSM10061 22 promoter (P_(wL))

Genomic DNA from Clostridium acetobutylicum ATCC824, C. beijerinckii NCIMB8052 and C. autoethanogenum DSM10061 was isolated using a modified method by Bertram and Dürre (Conjugal transfer and expression of streptococcal transposons in Clostridium acetobutylicum. Arch Microbiol 1989, 151: 551-557). A 100-ml overnight culture was harvested (6,000×g, 15 min, 4° C.), washed with potassium phosphate buffer (10 mM, pH 7.5) and suspended in 1.9 ml STE buffer (50 mM Tris-HCl, 1 mM EDTA, 200 mM sucrose; pH 8.0). 300 μl lysozyme (^(˜)100,000 U) were added and the mixture was incubated at 37° C. for 30 min, followed by addition of 280 μl of a 10% (w/v) SDS solution and another incubation for 10 min. RNA was digested at room temperature by addition of 240 μl of an EDTA solution (0.5 M, pH 8), 20 μl Tris-HCl (1 M, pH 7.5), and 10 μl RNase A. Then, 100 μl Proteinase K (0.5 U) were added and proteolysis took place for 1-3 h at 37° C. Finally, 600 μl of sodium perchlorate (5 M) were added, followed by a phenol-chloroform extraction and an isopropanol precipitation. DNA quantity and quality was inspected spectrophotometrically.

Acetone biosynthetic genes and the Wood-Ljungdahl cluster promoter were amplified by PCR with oligonucleotides in Tab. 8 using iProof High Fidelity DNA Polymerase (Bio-Rad Laboratories, Hercules, Calif. 94547, USA) and the following program: initial denaturation at 98° C. for 30 seconds, followed by 32 cycles of denaturation (98° C. for 10 seconds), annealing (50-62° C. for 30-120 seconds) and elongation (72° C. for 45 seconds), before a final extension step (72° C. for 10 minutes).

TABLE 8 Oligonucleotides used for amplification of acetone biosynthesis genes and promoter region SEQ_ID Description Oligonucleotide Name DNA Sequence (5′ to 3′) NO ThlA ThlA-Cac-NdeI-F GTTCATATGAAAGAAGTTGTAATAGC 23 ThlA-Cac-EcoRI-R CAAGAATTCCTAGCACTTTTCTAGC 24 CtfA, CtfB, Ctf-adc-cbei-KpnI-F CTAGGTACCAGGGAGATATTAAAATG 25 Adc operon Ctf-adc-cbei-BamH1-R CGTGGATCCTCTATATTGCTTTTATT 26 P_(WL) Pwoodlj-NotI-F AAGCGGCCGCAGATAGTCATAATAGTTCC 27 Pwoodlj-NdeI-R TTCCATATGAATAATTCCCTCCTTAAAGC 28

The amplified 573 bp promoter region of the Wood-Ljungdahl cluster (P_(WL)) was cloned into the E. coli-Clostridium shuttle vector pMTL 85141 (FJ797651.1; Nigel Minton, University of Nottingham, UK) [Heap J T, Pennington O J, Cartman S T, Minton N P. A modular system for Clostridium shuttle plasmids. J Microbiol Methods. 2009, 78: 79-85] using NotI and NdeI restriction sites and strain DH5α-T1^(R). The created plasmid pMTL85147 and the 1,194 bp PCR product of the thiolase gene were both cut with NdeI and EcoRI. A ligation was transformed into E. coli XL1-Blue MRF′ Kan resulting in plasmid pMTL85147-thlA. Subsequently, the amplified 2,177 bp PCR fragment of the ctfA-ctfB-adc operon from C. beijerinckii NCIMB 8052 was cloned into this vector using KpnI and BamHI and E. coli ABLE K, creating plasmid pMTL85147-thlA-ctfA-ctfB-adc. The insert of the resulting plasmid pMTL85147-thlA-ctfAB-adc was completely sequenced using oligonucleotides given in Tab. 9 and results confirmed that the acetone biosynthesis genes and promoter region were free of mutations (FIG. 5).

TABLE 9 Oligonucleotides used for sequencing SEQ_ID Oligonucleotide Name DNA Sequence (5′ to 3′) NO. Seq-ThlA-CtfAB-Adh 3539-4139 CAGAGGATGTTAATGAAGTC 29 Seq-ThlA-CtfAB-Adh 4140-4740 CTGTGCAGCAGTACTTGT 30 Seq-ThlA-CtfAB-Adh 4741-5341 GCAATGATACAGCTT 31 Seq-ThlA-CtfAB-Adh 5342-5942 AACCTTGGAATAGGACTTC 32 Seq-ThlA-CtfAB-Adh 6544-7144 TGTGAACTAATATGTGCAGA 33 M13 Forward GTAAAACGACGGCCAG 56 M13 Reverse CAGGAAACAGCTATGAC 57 Acetone Production in E. coli with Clostridial Acetone Pathway Genes:

To confirm the functionality of the constructed plasmid, a metabolic profile from a 5 ml overnight culture of E. coli ABLE K harbouring plasmid pMTL85147-thlA-ctfA-ctfB-adc were obtained using GC and HPLC, confirming acetone production.

To investigate this further, detailed growth experiments were carried out in triplicates with SD-8 minimal media containing 25 μg/ml chloramphenicol and E. coli XL-1 Blue MRF′ Kan carrying either plasmid pMTL 85147 (negative control) or expression plasmid pMTL 85147-thlA-ctfA-ctfB-adc (FIG. 42). While no acetone production could be observed in the negative control, an average maximum acetone production of 75.05 mg/L with an average dry biomass of 1.44 g/L was measured for the strain carrying the acetone plasmid.

Methylation of Expression Plasmid with Clostridial Acetone Pathway Genes:

Methylation of the acetone expression plasmid pMTL85147-thlA-ctfA-ctfB-adc was performed in vivo in E. coli using a synthesized hybrid Type II methyltransferase gene (SEQ_ID NO 35) designed from methyltransferase genes from C. autoethanogenum, C. ragsdalei and C. ljungdahlii. The methyltransferase (SEQ_ID NO 34) was synthesized and fused with an inducible lac promoter in vector pGS20 (ATG:biosynthetics GmbH, Merzhausen, Germany) (FIG. 6; SEQ_ID NO 49).

Both expression plasmid and methylation plasmid were transformed into same cells of restriction negative E. coli XL1-Blue MRF′ Kan, which is possible due to their compatible Gram-(−) origins of replication (high copy ColE1 in expression plasmid and low copy p15A in methylation plasmid). In vivo methylation was induced by addition of 1 mM IPTG, and methylated plasmids were isolated using QIAGEN Plasmid Midi Kit (QIAGEN GmbH, Hilden, Germany). The resulting mix was used for transformation experiments with C. autoethanogenum DSM23693 and C. ljungdahlii DSM 13528, but only the abundant (high-copy) expression plasmid has a Gram-(+) replication origin (repL) allowing to replicate in Clostridia.

Transformation of Methylated Acetone Expression Plasmid in C. autoethanogenum and C. ljungdahlii:

To make competent cells of C. autoethanogenum DSM23693 and C. ljungdahlii DSM 13528, a 50 ml culture (PETC media (Tab. 2) with steel mill gas and fructose as carbon source; 37° C.) was subcultured to fresh media for 3 consecutive days. These cells were used to inoculate 50 ml PETC media containing 40 mM DL-threonine at an OD_(600 nm) of 0.05. When the culture reached an OD_(600 nm) of 0.4, the cells were transferred into an anaerobic chamber and harvested at 4,700×g and 4° C. The culture was twice washed with ice-cold electroporation buffer (270 mM sucrose, 1 mM MgCl2, 7 mM sodium phosphate, pH 7.4) and finally suspended in a volume of 500 μl fresh electroporation buffer. This mixture was transferred into a pre-cooled electroporation cuvette with a 0.4 cm electrode gap containing ^(˜)1 μg of the methylated plasmid mix. Since an additional Type I restriction system was identified in the genome of C. ljungdahlii compared to C. autoethanogenum, 5 μl of a Type I restriction inhibitor (EPICENTRE Biotechnologies, Madison, Wis. 53713, USA) were added to the plasmid mix, which increased the transformation efficiency of C. ljungdahlii by 2-10 fold. The cells were mixed with plasmid and restriction inhibitor and immediately pulsed using a Gene pulser Xcell electroporation system (Bio-Rad Laboratories, Hercules, Calif. 94547, USA) with the following settings: 2.5 kV, 600Ω, and 25 μF. Time constants were between 3.7-5.1 ms. For regeneration, the culture was transferred in 5 ml special regeneration media (Tab. 10), which increased recovery of the cells, which was monitored at a wavelength of 600 nm using a Spectronic Helios Epsilon Spectrophotometer (Thermo Fisher Scientific Inc., Waltham Mass. 02454, USA) equipped with a tube holder. Once growth was observed (one doubling) the cells were harvested, suspended in 200 μl fresh media and plated on selective PETC plates with 15 μg/ml thiamphenicol (dissolved in 100% (v/v) dimethylfuran (DMF)) and 30 psi steel mill gas in the headspace. 50-200 colonies were visible after 4-6 days, which were used to inoculate 2 ml PETC media containing 15 μg/ml thiamphenicol (in DMF) and fructose and 30 psi steel mill gas as carbon source. When growth occurred, the culture was up-scaled into 5 ml and later 50 ml PETC media containing each 15 μg/ml thiamphenicol (in DMF) and 30 psi steel mill gas in the headspace as sole carbon source.

TABLE 10 Regeneration media Concentration per Media component 1.0 L of media NH₄Cl 1 g KCl 0.1 g MgSO₄•7H₂O 0.2 g KH₂PO₄ 0.2 g CaCl₂ 0.02 g Trace metal solution (see Tab. 2) 10 ml Wolfe's vitamin solution (see Tab. 2) 10 ml Yeast Extract 2 g Resazurin (2 g/L stock) 0.5 ml 2-(N-morpholino)ethanesulfonic acid (MES) 20 g Reducing agent 0.006-0.008% (v/v) Fructose 5 g Sodium acetate 0.25 g Fe(SO₄)₂(NH₄)₂•6H₂O 0.05 g Nitriolotriacetic Acid 0.05 g pH 5.7 Adjusted with NaOH Confirmation of Successful Transformation of C. autoethanogenum and C. ljungdahlii with Acetone Plasmid with Clostridial Acetone Pathway Genes:

To verify the DNA transfer, a plasmid mini prep was performed from 10 ml culture volume using Zyppy plasmid miniprep kit (Zymo Research, Irvine, Calif. 92614, USA). Since the quality of the isolated plasmid wasn't sufficient for a restriction digest due to Clostridial exonuclease activity [Burchhardt G and Dürre P, Isolation and characterization of DNase-deficient mutants of Clostridium acetobutylicum. Curr Microbiol 1990, 21: 307-311] with the isolated plasmid as template using primers ctf-adc-cbei-KpnI-F (Seq_ID no 25) and ctf-adc-cbei-BamH1-R (SEQ_ID NO 26) to confirm the presence of the plasmid (FIG. 7). PCR was carried out using iNtRON Maximise Premix PCR kit (Intron Bio Technologies) with the following conditions: initial denaturation at 94° C. for 2 minutes, followed by 35 cycles of denaturation (94° C. for 20 seconds), annealing (55° C. for 20 seconds) and elongation (72° C. for 135 seconds), before a final extension step (72° C. for 5 minutes).

To confirm the identity of the clones, genomic DNA was isolated using the protocol given above from 50 ml cultures of each C. autoethanogenum DSM23693 and C. ljungdahlii DSM13528. A PCR was performed against the 16s rRNA gene using oligonucleotides fD1 (SEQ_ID NO 36: CCGAATTCGTCGACAACAGAGTTTGATCCTGGCTCAG) and rP2 (SEQ_ID NO 37: CCCGGGATCCAAGCTTACGGCTACCTTGTTACGACTT) [Weisberg W G, Barns S M, Pelletier B A and Lane D J, 16S ribosomal DNA amplification for phylogenetic study. J Bacteriol 1990, 173: 697-703] and iNtRON Maximise Premix PCR kit (Intron Bio Technologies, Sangdaewon Joongwon Seognam Kyunggi, Korea) with the following conditions: initial denaturation at 94° C. for 2 minutes, followed by 35 cycles of denaturation (94° C. for 20 seconds), annealing (55° C. for 20 seconds) and elongation (72° C. for 60 seconds), before a final extension step (72° C. for 5 minutes). All sequences obtained had >99.9% identity against the 16s rRNA gene (rrsA) of C. autoethanogenum (Y18178, GI:7271109) and respectively C. ljungdahlii (CP001666.1; GI:300433347).

Acetone Production from CO and CO₂/H₂ with with Clostridial Acetone Pathway Genes in C. autoethanogenum and C. jungdahlii:

Growth experiments were carried out with transformed C. autoethanogenum DSM23693 and C. ljungdahlii DSM 13528 carrying plasmid pMTL85147-thlA-ctfAB-adc in 250 ml PETC media (Tab. 2; without fructose and yeast extract) in 1 l Schott bottles with rubber stoppers and 30 psi steel mill gas (collected from New Zealand Steel site in Glenbrook, NZ; composition: 44% CO, 32% N₂, 22% CO₂, 2% H₂) in the headspace as sole energy and carbon source. Acetone production was confirmed with both strains using HPLC and GC analysis. In Schott bottles acetone concentrations of around 0.3 g/l (6.5 mM) after 48 hours were achieved with both, C. autoethanogenum DSM23693 (FIGS. 8 and 10) and C. ljungdahlii DSM 13528 (FIGS. 9 and 10). Using appropriate conditions, the produced acetone can then be further converted to isopropanol. Acetone production of 153 mg/ml was also demonstrated on 30 psi biomass syngas (Range Fuels Inc., Broomfield, Colo.; composition: 29% CO, 45% H₂, 13% CH₄, 12% CO₂, 1% N₂) as sole energy and carbon source in 50 ml PETC media (Tab. 2; without fructose and yeast extract) in serum bottles with C. autoethanogenum DSM23693 (FIG. 11).

Expression of Heterologous with Clostridial Acetone Pathway Genes in C. autoethanogenum:

qRT-PCR experiments were performed to confirm successful expression of introduced genes thlA, ctfA, ctfB, and adc leading to acetone production in C. autoethanogenum and C. ljungdahlii. Signals for all genes could successfully be detected (FIGS. 52 and 53).

A 50-ml culture of each C. autoethanogenum and C. ljungdahlii harbouring plasmid pMTL85147-harvested by centrifugation (6,000×g, 5 min, 4° C.), snap frozen in liquid nitrogen and stored at −80° C. until RNA extraction. Total RNA was isolated using PureLink™ RNA Mini Kit (Invitrogen, Carlsbad, Calif., USA) and eluted in 100 μl of RNase-free water. After DNase I treatment (Roche Applied Science, Indianapolis, Ind., USA), the reverse transcription step was then carried out using SuperScript III Reverse Transcriptase Kit (Invitrogen, Carlsbad, Calif., USA). RNA was checked using an Agilent Bioanalyzer 2100 (Agilent Technologies, Santa Clara, Calif., USA), Qubit Fluorometer (Invitrogen, Carlsbad, Calif., USA) and by gel electrophoresis. A non-RT control was performed for every primer pair. All qRT-PCR reactions were performed in duplicates using a MyiQ Single Colour Detection System (Bio-Rad Laboratories, Carlsbad, Calif., USA) in a total reaction volume of 15 μl with 25 ng of cDNA template, 67 nM of each primer (Table 17), and 1× iQ SYBR Green Supermix (Bio-Rad Laboratories, Carlsbad, Calif., USA). The reaction conditions were 95° C. for 3 min, followed by 40 cycles of 95° C. for 15 s, 55° C. for 15 s and 72° C. for 30 s. For detection of primer dimerisation or other artifacts of amplification, a melting-curve analysis was performed immediately after completion of the qPCR (38 cycles of 58° C. to 95° C. at 1° C./s). Two housekeeping genes (Guanylate kinase and formate tetrahydrofolate ligase) were included for each cDNA sample for normalization. Derivation of relative gene expression was conducted using Relative Expression Software Tool (REST©) 2008 V2.0.7 (38). Dilution series of cDNA spanning 4 log units were used to generate standard curves and the resulting amplification efficiencies to calculate concentration of mRNA.

TABLE 17 Oligonucleotides for qRT-PCR Oligonucleotide SEQ_ID Target Name DNA Sequence (5′ to 3′) NO. Guanylate kinase (gnk) GnK-F TCAGGACCTTCTGGAACTGG 5 GnK-R ACCTCCCCTTTTCTTGGAGA 6 Formate tetrahydrofolate FoT4L-F CAGGTTTCGGTGCTGACCTA 7 ligase (FoT4L) FoT4L-F AACTCCGCCGTTGTATTTCA 8 Thiolase A thlA-RT-F TTGATGAAATGATCACTGACGGATT 64 thlA-RT-R GAAATGTTCCATCTCTCAGCTATGT 65 Acetoacetyl-CoA: Acetate ctfB-RT-F CTAATACGAGGAGGACATGTTGATG 66 CoA-transferase B ctfB-RT-R CACCCATACCTGGGACAATTTTATT 67 Acetoacetyl-CoA: Acetate ctfA-RT-F GGGCTGCTACTAAAAATTTCAATCC 68 CoA-transferase A ctfA-RT-R CAGGAGTCATTATGGCATCTCTTTT 69 Acetoacetate decarboxylase adc-RT-F TAGTACCAGAGCCACTTGAATTAGA 70 adc-RT-R GGAATAGCTTGACCACATTCTGTAT 71 Conversion of Acetone to Isopropanol by C. autoethanogenum, C. Ljungdahlii, and C. ragsdalei:

Acetone can be further converted to isopropanol by action of an alcohol dehydrogenase. However, only few microorganisms such as C. beijerinckii NRRL-B593 are described to produce isopropanol, and acetone-to-isopropanol converting enzymes are very rare in nature. So far only two secondary alcohol dehydrogenases have been identified and described to date, from C. beijerinckii NRRL-B593 [Ismaiel A A, Zhu C X, Colby G D, Chen J S: Purification and characterization of a primary-secondary alcohol dehydrogenase from two strains of Clostridium beijerinckii. J Bacteriol 1993, 175: 5097-5105] (SEQ_ID NO 38-39) and Thermoanaerobacter brockii [Peretz M and Burstein Y: Amino acid sequence of alcohol dehydrogenase from the thermophilic bacterium Thermoanaerobium brockii. Biochemistry. 1989, 28:6549-6555] (SEQ_ID NO 40-41).

Therefore, a collection of microorganisms—acetogenic bacteria, acetone and isopropanol producing Clostridia and E. coli—were tested for their ability to convert acetone to isopropanol (Tab. 11).

TABLE 11 Addition of acetone to growing cultures of various microorganisms. Directly after acetone addition End of growth Acetone Isopropanol Acetone Isopropanol Organism/Sample Description Media [g/l] [g/l] [g/l] [g/l] Acetobacterium Acetogenic PETC (pH 10.81 0 10.83 0 woodii species 8.2) DSM1030 Clostridium PETC (pH 10.07 0 10.09 0 aceticum 7.4) DSM1496 C. PETC (pH 9.25 0 1.13 8.03 autoethanogenum 5.9) DSM23693 C. carboxidivorans 10.43 0 10.34 0 DSM15243 C. ljungdahlii 10.23 0 3.73 6.54 DSM13528 C. ragsdalei 11.25 0 9.94 1.34 ATCC BAA-622 C. beijerinckii Isopopanol RCM 9.96 0 7.65 2.54 NRRL-B593 producing species C. beijerinckii Acetone 10.49 0 10.59 0 NCIMB8052 producing C. acetobutylicum species 10.80 0 10.91 0 ATCC824 Escherichia coli LB + 11.67 0 11.71 0 DH5 (Invitrogen) glucose Blank media Control PETC 10.51 0 10.55 0

All cultures were inoculated to an OD_(600 nm) of 0.1 in 50 ml appropriate media containing a heterotrophic carbon source and 30 psi steel mill gas. The cultures were allowed to double (OD_(600 nm)=0.2) before acetone was added. A sample was taken and analyzed by HPLC and GC immediately after acetone addition and again at the end of growth (which were followed by measuring the optical density). Results are summarized in Tab. 11. Blank media was used as negative control.

As expected, isopropanol producing strain C. beijerinckii NRRL-B593 [George H A, Johnson J L, Moore W E C, Holdeman L V, Chen J S: Acetone, isopropanol, and butanol production by Clostridium beijerinckii (syn. Clostridium butylicum) and Clostridium aurantibutyricum. Appl Environ Microbiol 45: 1160-1163] had the ability to reduce externally added acetone to isopropanol by action of its alcohol dehydrogenase. A different strain of C. beijerinckii, NRCIMB8052, which lacks this enzyme wasn't able to convert acetone to isopropanol, as the acetone producing C. acetobutylicum ATCC-824. The same is also true for E. coli.

Surprisingly, three carboxydotrophic acetogenic bacteria C. autoethanogenum, C. ljungdahlii, and C. ragsdalei, which form a subcluster within the Clostridial rRNA Homology Group I, were found to be able to convert acetone to isopropanol as well, while all other acetogenic bacteria tested couldn't utilize acetone (Tab. 11). Conversion of different amounts of acetone to isopropanol by C. autoethanogenum was then tested using different concentrations (Tab. 12).

TABLE 12 Conversion of different concentrations of acetone to isopropanol by cultures of C. autoethanogenum DSM23693. Acetone [g/l] Acetone [g/l] Isopropanol [g/l] added left at end of growth left at end of growth 0 0 0 1.66 0.22 1.48 9.25 1.13 8.03 26.13 17.82 8.39 50.01 43.30 6.95

A reactor study with C. autoethanogenum DSM23693 was performed to demonstrate effective conversion of acetone to isopropanol at high rates. The reactor was set-up as described above. Once in continuous mode with stable biomass and metabolite production, acetone was added to both the bioreactor and the feed medium. Acetone was spiked into the reactor to a certain level, which was then obtained by continuous feeding. Initially, 1 g/L acetone was added, once the metabolite concentrations had stabilised, the concentration was increased to 5 g/L, 15 g/I, and in a second experiment to 20 g/L. Even at high concentrations of 20 g/L the culture converted all acetone to isopropanol at high rate demonstrating that the identified primary:secondary alcohol dehydrogenase is highly effective (FIG. 74).

Identification of a Novel Alcohol Dehydrogenase in C. autoethanogenum, C. Ljungdahlii, and C. ragsdalei:

To confirm that the conversion of acetone to isopropanol by C. autoethanogenum is driven enzymatically, enzyme assays were carried out with crude extract of C. autoethanogenum 23693, C. beijerinckii NRRL-B593, and C. carboxidivorans DSM15243 according to Ismaiel et al [Ismaiel A A, Zhu C X, Colby G D, Chen J S: Purification and characterization of a primary-secondary alcohol dehydrogenase from two strains of Clostridium beijerinckii. J Bacteriol 1993, 175: 5097-5105]. Crude extracts were obtained by sonication and lysozyme treatment (100,000 U/ml) of late exponential cultures. Cell debris was removed by centrifugation and protein concentrations was determined using the Pierce BCA protein assay—reducing agent compatible (Thermo Fisher Scientific Inc., Waltham Mass. 02454, USA). The assay mixture (1 ml) contained 50 mM Tris buffer (pH 7.5), 1 mM dithiothreitol (DTT), and 0.2 mM NAD(P)H. The reaction was started by adding 10 mM of the substrate acetone (from a 10-fold dilution in water) and followed spectrophotometrically with a Spectramax M2 (Molecular Devices, Inc., Sunnyvale, Calif. 94089-1136, USA) at a wavelength of 365 nm. H₂O was used as negative control instead of crude extract and respectively acetone. Enzyme activity could be detected with crude extracts of both C. beijerinckii and C. autoethanogenum and NADPH (not with NADH), but not with crude extracts of C. carboxidivorans DSM15243 or H₂O (with both NADPH and NADH). This demonstrates that the conversion of acetone to isopropanol by C. autoethanogenum is driven enzymatically, and as no activity was detected with NADH, the enzyme appears to be NADPH-dependent.

By sequencing and careful analysis, a novel alcohol dehydrogenase gene/enzyme was identified in all three strain, C. autoethanogenum, C. ljungdahlii, and C. ragsdalei (FIG. 1; SEQ_ID NO. 1-4). The amino acid sequence was found to be identical in all three species and share some homology to the primary-secondary alcohol dehydrogenase of C. beijerinckii NRRL-B593 (87%) and T. brockii ATCC 53556 (76%) (Tab. 13). Compared to the well-described secondary alcohol dehydrogenase of C. beijerinckii NRRL-B593 [Ismaiel A A, Zhu C X, Colby G D, Chen J S: Purification and characterization of a primary-secondary alcohol dehydrogenase from two strains of Clostridium beijerinckii. J Bacteriol 1993, 175: 5097-5105], a total of 49 amino acids exchanges were found. 4 amino acids of the catalytic centre of the protein are conserved, however, other amino acids in the catalytic domain are not (FIG. 1). A motif search predicted the novel alcohol dehydrogenase gene/enzyme to be zinc and NAD(P)H dependent. The respective genes coding for the novel alcohol dehydrogenase was found to be 98% identical within the 3 species C. autoethanogenum, C. ljungdahlii, and C. ragsdalei, but only 82% identical to the one from C. beijerinckii and 72% identical to the one from T. brockii (Tab. 14).

TABLE 13 Comparison of amino acid sequences of novel alcohol dehydrogenase and known secondary alcohol dehydrogenases Accession Organism Description Seq ID number Reference Score e-Value Identity C. — SEQ_ID — — 717 bits 0 351/351 autoethanogenum NO. 1 (1852) (100%) C. ljungdahlii zinc-containing SEQ_ID YP_003780646.1 — 717 bits 0 351/351 alcohol NO. 1 (1852) (100%) dehydrogenase C. ragsdalei — SEQ_ID — — 717 bits 0 351/351 NO. 1 (1852) (100%) C. beijerinckii NADP- SEQ_ID P25984.2 Ismaiel et 630 bits 7E−179 302/351 NRRL B-593 dependent NO. 38 al., 1993 (1626) (87%) alcohol dehydrogenase T. brockii ATCC NADP- SEQ_ID P14941.1 Peretz and 557 bits 7E−157 264/351 53556 dependent NO. 40 Burstein, (1436) (76%) alcohol 1989 dehydrogenase

TABLE 14 Comparison of nucleic acid sequences of novel alcohol dehydrogenase and known secondary alcohol dehydrogenases Accession Organism Description Seq ID number Reference Score e-Value Identity C. SEQ_ID — — 1905 bits 0 1056/1056 autoethanogenum NO. 2 (2112) (100%) C. ljungdahlii zinc-containing SEQ_ID CP001666.1 — 1900 bits 0 1055/1056 alcohol NO. 3 (2106) (99%) dehydrogenase C. ragsdalei SEQ_ID — — 1803 bits 0 1033/1056 NO. 4 (1998) (98%) C. beijerinckii NADP- SEQ_ID AF157307.2 — 558 bits 0 861/1056 NRRL B-593 dependent NO. 39 (618) (82%) alcohol dehydrogenase T. brockii alcohol SEQ_ID X64841.1 — 562 bits 3.00E−155 757/1053 dehydrogenase NO. 41 (622) (72%) Expression Studies of the Novel Alcohol Dehydrogenase from C. autoethanogenum

To identify, if the gene encoding the novel alcohol dehydrogenase is active during a normal fermentation with C. autoethanogenum, as well as identifying potential promoter regions for gene-overexpression, a qRT-PCR study with a over 250 genes was performed.

Samples were taken from a typical 1.5 l fed-batch fermentation run as described above over the whole growth (4 days). The samples were harvested by centrifugation (6,000×g, 5 min, 4° C.) and the cell pellet snap frozen in liquid nitrogen and stored at −80° C. until use. RNA was isolated by thawing the cell pellet on ice and suspending it in 100 μL of lysozyme solution (50,000 U lysozyme, 0.5 μL 10% SDS, 10 mM Tris-HCl, 0.1 mM EDTA; pH 8). After 5 min, 350 μL of lysis buffer (containing 10 μL of 2-mercaptoethanol) was added. The cell suspension was mechanistically disrupted by passing five times through an 18-21 gauge needle. RNA was then isolated using PureLink™ RNA Mini Kit (Invitrogen, Carlsbad, Calif. 92008, USA) and eluted in 100 μL of RNase-free water. The RNA was checked via PCR and gel electrophoresis and quantified spectrophotometrically, and treated with DNase I (Roche) if necessary. The reverse transcription step was carried out using SuperScript III Reverse Transcriptase Kit (Invitrogen, Carlsbad, Calif. 92008, USA). RT-PCR reactions were performed in MyiQ Single Colour Real-Time PCR Detection System (Bio-Rad Laboratories, Hercules, Calif. 94547, USA) in a reaction volume of 15 μL with 25 ng of cDNA template, 67 nM of each primer (Tab. 15), and 1× iQ SYBR Green Supermix (Bio-Rad Laboratories, Hercules, Calif. 94547, USA). Guanylate kinase (GnK) and formate tetrahydrofolate ligase (FoT4L) were used as housekeeping gene and non-template controls were included. The reaction conditions were 95° C. for 3 min, followed by 40 cycles of 95° C. for 15 s, 55° C. for 15 s and 72° C. for 30 s. A melting-curve analysis was performed immediately after completion of the qRT PCR (38 cycles of 58° C. to 95° C. at 1° C./s), for detection of primer dimerisation or other artifacts of amplification. Data on the expression level was computed in the form of threshold cycle (C_(t)) values based on PCR base line subtracted curve fit method as calculated by the Biorad iQ5 2.0 software. The raw C_(t) values were further analyzed using Relative Expression Software Tool (REST©) 2008 V2.0.7.

TABLE 15 Oligonucleotides for RT-PCR Oligonucleotide SEQ_ID Target Name DNA Sequence (5′ to 3′) NO. Guanylate kinase (gnk) GnK-F TCAGGACCTTCTGGAACTGG 5 GnK-R ACCTCCCCTTTTCTTGGAGA 6 Formate tetrahydrofolate FoT4L-F CAGGTTTCGGTGCTGACCTA 7 ligase (FoT4L) FoT4L-F AACTCCGCCGTTGTATTTCA 8 CO dehydrogenase (acsA) acsA-F ACAAGATGGGGTCGAAACAGTTTGG 9 acsA-R TGGCACTGGACTTACTCTACATGGG 10 Formyl-THF synthase (fhs) fhs-F TATTTCCGAAGATGATATTGAATTGTAT 11 GG fhs-R TCCAGCAGGTGTTGGGTTTATAGC 12 Formimido-THF fchA-F AGCTGCAACTCCTGGTGGAGGC 13 cyclodeaminase (fchA) fchA-R GCCTTTTACCTTTTCGTCATACTGTGC 14 Methylene-THF folD-F GCTTACATTAGTAAGAGTTGGAGCAAA 15 dehydrogenase CG formyl-THF cyclohydrolase folD-R ACTTGTCCTGTGATATATCTGCTGGTAG 16 (folD) C alcohol dehydrogenase (adh) Adh-F GGTCCTTATGATGCGATTGTACATCC 17 Adh-R GCTATTTCACCTACAGCTTCATGGCC 18

The result of the qRT-PCR study showed, that the gene for the novel alcohol dehydrogenase is expressed over the whole growth on a relatively constant level and only ceases at end of growth (FIG. 2). Compared to over 200 genes chosen from every part of the metabolism, the alcohol dehydrogenase gene belongs to the top 50 expressed genes. The highest gene expression of all genes analyzed showed the genes of the Wood-Ljungdahl operon, with an mRNA level of more than 10-fold higher than the alcohol dehydrogenase gene (FIG. 2). The respective promoter (SEQ_ID NO 22) region is therefore ideal to over-express genes, such as the genes for acetone biosynthesis enzymes and an alcohol dehydrogenase gene, although in the case of over-expression of an alcohol dehydrogenase gene native to the micro-organisms it may require additional genetic modification to ensure sufficient co-factor availability. This could include, for example, (over-)expression of further genes to increase the NADPH pool such as transhydrogenase, elimination of competing NADPH consuming reactions, or protein engineering to change the co-factor requirement to NADH. Other useful promoter regions identified for gene over-expression include the promoter region of F₁F_(o)-ATPase operon (SEQ_ID NO 51), Rnf complex operon (SEQ_ID NO 52), and Pyruvate:ferredoxin oxidoreductase (SEQ_ID NO 53).

Isopropanol Production from CO and CO₂/H₂ by C. autoethanogenum and C. ljungdahlii with Expression Plasmid Containing Clostridial Acetone Genes

The 250 ml Schott bottle cultures of recombinant strains of C. autoethanogenum DSM23693 and C. Ijungdahlii DSM 13528 carrying acetone expression plasmid pMTL85147-thlA-ctfAB-adc were shown to produce acetone, but no isopropanol could be detected (FIG. 8+9). This might be due to the lack of reducing power at end of growth, due to the given static conditions in Schott bottles, where CO gets depleted from the headspace and is not constantly fed like in a fed-batch or continuous fermentation process. Reducing equivalents such as NAD(P)H or ferredoxin gets generated from CO, but are also consumed for ethanol production, which already occurs during exponential and early stationary growth. At this point is the concentration of produced acetone, which is needed as precursor for isopropanol production, is still relatively low.

Therefore, both cultures were re-gassed with 30 psi fresh steel-mill gas after 48 h of growth and also re-inoculated. While biomass didn't increase much further, some of the produced acetone got converted into isopropanol within 24 hours (Tab. 16).

TABLE 16 Conversion of acetone to isopropanol by cultures of C. autoethanogenum DSM23693 and C. ljungdahlii DSM 13528 Acetone [mg/l] Isopropanol [mg/l] After After Organism After 48 h 72 hours After 48 h 72 hours C. autoethanogenum + 220 295 0 25 pMTL85147-thlA-ctfAB- adc C. ljungdahlii + 171 175 0 5 pMTL85147-thlA-ctfAB- adc

In a fermentation system with constant supply of CO, sufficient reducing power is present for continuous production of isopropanol from CO or CO/H₂ and both acetone and isopropanol were produced in a respective fermentation run with C. autoethanogenum DSM23693 carrying acetone expression plasmid pMTL85147-thlA-ctfAB-adc.

Cloning of Novel Alcohol Dehydrogenase

The novel alcohol dehydrogenase was cloned into the acetone expression plasmid and put under control of the Wood-Ljungdahl promoter for gene over-expression and test of functionality in E. coli.

Alcohol dehydrogenase was amplified from isolated C. autoethanogenum DSM10061 chromosomal DNA using oligonucleotides SecAdh-SalI-F (SEQ_ID NO 54: TATTTGTCGACTTAGGAGGTTCTATTATGAAAGG) and SecAdh-XhoI-R (SEQ_ID NO 55: AAAACTCGAGACATTTTTTTAATGCGACAG). The 1129 bp PCR fragment was cloned into plasmid pMTL85147-thlA-ctfAB-adc using SalI and XhoI and E. coli XL-1 Blue MRF′ Kan. The resulting plasmid pMTL85147-thlA-ctfA-ctfB-adc-adh (SEQ_ID NO 48; FIG. 43) was completely sequenced using oligonucleotides given in Tab. 9 and results confirmed that the isopropanol biosynthesis genes and promoter region were free of mutations (FIG. 41).

Production of Isopropanol with Novel Alcohol Dehydrogenase from C. autoethanogenum in E. coli

To further test the functionality of the novel alcohol dehydrogenase from C. autoethanogenum, growth experiments were carried out using E. coli XL-1 Blue MRF′ Kan expressing only the acetone biosynthesis genes (carrying plasmid pMTL 85147-thlA-ctfA-ctfB-adc) and expressing the acetone biosynthesis genes plus the novel alcohol dehydrogenase (carrying plasmid pMTL85147-thlA-ctfA-ctfB-adc-adh) in 100 ml SD-8 minimal media with chloramphenicol (FIG. 42).

While no isopropanol could be detected with the strain carrying the acetone plasmid, an average maximum of 32.7 mg/L isopropanol was measured with the strain additionally expressing the novel alcohol dehydrogenase from C. autoethanogenum.

Identification of Genes from Lactococcus lactis and Saccharomyces cerevisiae that Confer Novel Activity Towards Acetone or Isopropanol in C. autoethanogenum

In addition to the Clostridial acetone and isopropanol pathway, two enzymes an Alpha-ketoisovalerate decarboxylase (KivD) from Lactococcus lactis and an Alcohol dehydrogenase (Adh2) from Saccharomyces cerevisiae (Tab. 18) were identified that confer activity towards acetone and isopropanol production in C. autoethanogenum. Those two enzymes haven't been reported to be involved in acetone or isopropanol production or have catalytic functions on any of the precursors in the Clostridial acetone and isopropanol pathway. Heterologous expression of these proteins in E. coli (Atsumi et al., 2008. Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels. Nature, 451: 86-90) or other organisms like Corynebacterium glutamicum (Blombach et al., 2011. Corynebacterium glutamicum tailored for efficient Isobutanol production. Appl. Environ. Microbiol. 77: 3300-10) or Clostridium cellulolyticum (Higashide W., et al. 2011. Metabolic Engineering of Clostridium cellulolyticum for Production of Isobutanol from Cellulose. Appl. Environ. Microbiol. 77: 2727-33) led to production of branched-chain higher alcohols like isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol from amino acid precursors, but neither acetone nor isobutanol was reported. Expression of codon-optimized Alpha-ketoisovalerate decarboxylase (KivD) from Lactococcus lactis alone or a combination of codon optimized Alpha-ketoisovalerate decarboxylase (KivD) from Lactococcus lactis and an Alcohol dehydrogenase (Adh2) from Saccharomyces cerevisiae in C. autoethanogenum however, led surprisingly to production of acetone and isopropanol.

TABLE 18 Sequences from Lactococcus lactis and Saccharomyces cerevisiae that confer novel activity towards acetone or isopropanol in C. autoethanogenum L. lactis Description nucleic acid amino acid Alpha-ketoisovalerate SEQ_ID No. 72 SEQ _ID No. 73; decarboxylase (KivD) AJ746364 YP_003353820.1 S. cerevisiae nucleic acid amino acid Alcohol dehydrogenase (Adh2) SEQ_ID No. 74 SEQ_ID No. 75; NC_001145.2, AAA34408.1 GeneID: 855349 Construction of Expression Plasmid with Alpha-Ketoisovalerate Decarboxylase (KivD) from Lactococcus lactis and Alcohol Dehydrogenase (Adh2) from Saccharomyces cerevisiae

The Alpha-ketoisovalerate decarboxylase (decarboxylase; KivD) from L. lactis, and Alcohol dehydrogenase (Adh2) from S. cerevisiae (Tab. 18) were codon-optimised by ATG:Biosynthetics GmbH (Merzhausen, Germany) and flanked by NdeI and KpnI restriction sites for further sub-cloning. The Phosphiotransacetylase/Acetate kinase operon promoter of C. autoethanogenum was used for expression of target genes. All DNA sequences used are given in Tab. 19.

TABLE 19 Sequences used for expression plasmid with Alpha-ketoisovalerate decarboxylase (KivD) from Lactococcus lactis and Alcohol dehydrogenase (Adh2) from Saccharomyces cerevisiae SEQ_ID Description Source NO. Alpha-ketoisovalerate Codon optimized 76-78 decarboxylase (KivD) and Alcohol dehydrogenase (Adh2) Phosphotransacetylase/Acetate Clostridium autoethanogenum 79 kinase operon promoter region DSM10061

The promoter region of the phosphotransacetylase-acetate kinase operon (P_(pta-ack)) was amplified using primers Ppta-ack-NotI-F (Seq. ID. No. 80: GAGCGGCCGCAATATGATATTTATGTCC) and Ppta-ack-NdeI-R (Seq. ID. No. 81: TTCCATATGTTTCATGTTCATTTCCTCC) and cloned into the E. coli-Clostridium shuttle vector pMTL 85141 (FJ797651.1; Nigel Minton, University of Nottingham, UK) [Heap J T, Pennington O J, Cartman S T, Minton N P. A modular system for Clostridium shuttle plasmids. J Microbiol Methods. 2009, 78: 79-85] using NotI and NdeI restriction sites and strain XL1-Blue MRF′ Kan.

The antibiotic resistance gene in the created plasmid pMTL85145 was subsequently replaced with an erythromycin resistance gene from pMTL 82254 (FJ797646.1; Nigel Minton, University of Nottingham, UK) [Heap J T, Pennington O J, Cartman S T, Minton N P. A modular system for Clostridium shuttle plasmids. J Microbiol Methods. 2009, 78: 79-85] using FseI and PmeI restriction sites and strain XL1-Blue MRF′ Kan.

The created plasmid pMTL85245 (Seq. ID. No. 80) and the 2746 bp codon-optimised product of the decarboxylase and alcohol dehydrogenase (Adh2) gene cluster were both cut with NdeI and KpnI. A ligation was transformed into E. coli XL1-Blue MRF′ Kan resulting in plasmid pMTL85245-kivd-adh2 (Seq. ID. No. 83; FIG. 63). The insert of the resulting plasmid pMTL85245-kivd-adh was completely sequenced using oligonucleotides given in Tab. 20 and results confirmed that genes and promoter region were free of mutations.

The kivD gene alone was amplified using primer pair M13 Reverse (Seq. ID. 57: CAGGAAACAGCTATGAC) and Adh_seqR1 (Seq. ID. 85; Tab. 16). The 2635 bp PCR fragment of KivD was cloned into the E. coli-Clostridium shuttle vector pMTL 85245 using NdeI and EcoRI restriction sites and strain E. coli XL1-Blue MRF′ Kan, creating plasmid pMTL85245-kivd (Seq. ID No. 84; FIG. 64). The insert of the resulting plasmid pMTL85245-kivd was completely sequenced using oligonucleotides given in Tab. 20 and results confirmed that the acetone biosynthesis gene was free of mutations.

TABLE 20 Oligonucleotides used for sequencing Adh_seqR1 TCAGTTCCCTGTGGAATGTGTGC Seq. ID. No. 85 Kivd_seqR2 TCAGTAGCACCGAAAGATTCAG Seq. ID. No. 86 Kivd_seqR3 AGTGCCTCATCTACTGAACTC Seq. ID. No. 87 -ori_F ATTAGTTTAAACACGCCAGCAACGCGGCCTTTTTAC Seq. ID. No. 88 ctfAB_seqR1 TCCTATTCCAAGGTTTACGAGTTGGTC Seq. ID. No. 89 ctfAB_seqR2 ACCCCCAACCATAATTGTCATGCCATC Seq. ID. No. 90 ctfAB_seqR3 TGCAAGAGCAAACTCATCTTGTTCTTC Seq. ID. No. 91 P-thl-ctfAB_R2 AGGGTGCGGCCGCGATTCATATATCCATAATCTTTAAGTTATC Seq. ID. No. 92 Expression of Codon-Optimized Genes for Alpha-Ketoisovalerate Decarboxylase (KivD) from Lactococcus lactis and Alcohol Dehydrogenase (Adh2) from Saccharomyces cerevisiae in C. autoethanogenum for Production of Acetone and Isopropanol

Constructed expression plasmids pMTL85245-kivd-adh2 and pMTL85245-kivd were transformed into E. coli strain JW3350-2 and prepared for transformation in C. autoethanogenum DSM23693, which was performed as described above. While in E. coli harbouring the two plasmids, neither acetone nor isopropanol could be detected (but higher branched-chain alcohols such as isobutanol as described in the literature), in C. autoethanogenum, both acetone and isopropanol could be detected. In serum bottle experiments, highest isopropanol concentrations from CO-containing steel mill gas were 0.050-0.064 g/L for both expression plasmids (FIGS. 65 and 66).

Production of Acetone and Isopropanol with a Combination of Clostridial Pathway Genes and Alpha-Ketoisovalerate Decarboxylase (KivD) from Lactococcus lactis and Alcohol Dehydrogenase (Adh2) from Saccharomyces cerevisiae

Without wanting to be bound by any particular theory, the inventors believe that the codon-optimized alpha-ketoacid decarboxylase Kivd from Lactococcus lactis has activity converting acetoacetate to acetone, as the Clostridial acetoacetate decarboxylase, while the codon-optimized alcohol dehydrogenase Adh2 from Saccharomyces cerevisiae have activity converting acetone to isopropanol as the novel primary:secondary alcohol dehydrogenase identified or the primary:secondary alcohol dehydrogenase from Clostridium beijkerickii. To test this hypothesis several combinations of Clostridial acetone/isopropanol pathway genes and the alpha-ketoacid decarboxylase Kivd from Lactococcus lactis and alcohol dehydrogenase Adh2 from Saccharomyces cerevisiae have been created and tested within E. coli and C. autoethanogenum demonstrating production of acetone and isopropanol.

Construction of Expression Plasmids with Different Gene Combinations

Based on the constructed expression plasmids pMTL85147-thlA-ctfA-ctfB-adc, pMTL85245-kivd-adh2 and pMTL85245-kivd, new combinations were constructed.

A 3122 bp P_(WL)-thlA-ctfAB fragment was amplified from plasmid pMTL85147-thlA-ctfA-ctfB-adc using oligonucleotides P-thl-ctfAB_F2 (Seq. ID. No. 93: ATCTTCTGCAGGGCCGCAGATAGTCATAATAGTTCCAG) and P-thl-ctfAB_R2 (Seq. ID. No. 94: AGGGTGCGGCCGCGATTCATATATCCATAATCTTTAAGTTATC). The amplified fragment was cloned into plasmid pMTL 85245-kivd using PstI and NotI restriction sites and strain E. coli XL1-Blue MRF′ Kan, creating plasmid pMTL85245-P_(WL)-thlA-ctfAB-kivd (Seq. ID. No. 95; FIG. 67). The insert of the resulting plasmid pMTL85245-P_(WL)-thlA-ctfAB-kivd was completely sequenced using oligonucleotides given in Tab. 9 and 20 and confirmed that the plasmid was free of mutations.

The Adh2 gene was amplified from plasmid pMTL85245-kivd-adh2 using primer pair adh_F (Seq. ID. No. 96: ACGTTGGATCCAGGAGGAACAAAGATGAGTATACC) and P-kivd-adh_R (Seq. ID. No. 97: AGCGTCCATGGCCTTATTTACTTGTATCTACAACATATC). The 1084 bp PCR fragment was cloned into the plasmid pMTL85147-thlA-ctfAB-adc using BamHI and NcoI restriction sites and strain E. coli XL1-Blue MRF′ Kan, creating plasmid pMTL85147-thlA-ctfAB-adc-adh2 (Seq. ID. No. 98; FIG. 68). The created plasmid pMTL85147-thlA-ctfAB-adc-adh2 and a 1625 bp fragment of the repL gene from pMTL83151 (FJ797647.1; Nigel Minton, University of Nottingham, UK) [Heap J T, Pennington O J, Cartman S T, Minton N P. A modular system for Clostridium shuttle plasmids. J Microbiol Methods. 2009, 78: 79-85] were both cut with FseI and AscI. A ligation was performed resulting in plasmid pMTL83147-thlA-ctfAB-adc-adh2. The insert of the resulting plasmid pMTL83147-thlA-ctfAB-adc-adh2 was completely sequenced using oligonucleotides given in Tab. 9 and 20 and results confirmed that the fragment was mutation free.

Oligonucleotides P-kivd-adh_F (Seq. ID. No. 99: ATATTGGATCCACAGCTATGACCGCGGCCGCAATATG) and P-kivd-adh_R (Seq. ID. No. 100: AGCGTCCATGGCCTTATTTACTTGTATCTACAACATATC) were used to amplify a 3266 bp PCR fragment of P_(pta-ack)-kivd-adh2 from plasmid pMTL85245-kivd-adh2, which was then cloned into the plasmid pMTL85147-thlA-ctfAB-adc using BamHI and NcoI restriction sites and strain E. coli XL1-Blue MRF′ Kan, creating plasmid pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2 (Seq. ID. 101; FIG. 69). The created plasmid pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2 and a 1625 bp fragment of the repL gene from pMTL83151 (FJ797647.1; Nigel Minton, University of Nottingham, UK) [Heap J T, Pennington O J, Cartman S T, Minton N P. A modular system for Clostridium shuttle plasmids. J Microbiol Methods. 2009, 78: 79-85] were both cut with FseI and AscI. A ligation was performed resulting in plasmid pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2. The insert of the resulting plasmid pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2 was completely sequenced using oligonucleotides given in Tab. 9 and results confirmed that the plasmid was free of mutations.

Production of Acetone and Isopropanol in C. autoethanogenum Using Different Gene Combinations

Methylation of the newly constructed expression plasmids pMTL85147-thlA-ctfA-ctfB-adc, pMTL83147-thlA-ctfAB-adc-adh2 and pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2 were performed in vivo in E. coli using a synthesized hybrid Type II methyltransferase gene (SEQ_ID NO 35) designed from methyltransferase genes from C. autoethanogenum, C. ragsdalei and C. ljungdahlii and transformed into C. autoethanogenum DSM23693 as described above.

All plasmid construct were tested in E. coli and C. autoethanogenum DSM23693 using serum bottle experiments with sugar (E. coli) or CO-containing steel mill gas (C. autoethanogenum) as sole substrate. With all combinations tested, acetone and isopropanol production was measured when expressed heterologously in C. autoethanogenum, while in E. coli acetone production only occurred with few combinations and an alcohol dehydrogenase gene was needed for isopropanol production (Tab. 21). The results presented show that both, in E. coli as well as C. autoethanogenum, the codon-optimized Alpha-ketoacid decarboxylase Kivd from Lactococcus lactis is able to replace the Clostridial acetoacetate decarboxylase and catalyse the conversion of acetoacetate to acetone (FIG. 4). In C. autoethanogenum, acetone and isopropanol production even occurred with expressing the decarboxylase as only heterologous gene, indicating CoA-transferase activity. FIG. 4 illustrates the proposed pathway and Tab. 21 of acetone and isopropanol formation from CO and FIG. 73 gives an overview of combinations of Clostridial pathway genes and codon-optimized genes for Alpha-ketoacid decarboxylase Kivd from L lactis and Alcohol dehydrogenase Adh2 from S. cerevisiae tested in E. coli and C. autoethanogenum.

Production of acetone and isopropanol with C. autoethanogenum DSM23693 and plasmids pMTL85245-P_(WL)-thlA-ctfAB-kivd, pMTL83147-thlA-ctfAB-adc-adh2 and pMTL83147-thlA-ctfAB-adc-P_(pta-ack)-kivd-adh2 from CO-containing steel mill gas is shown in FIGS. 70, 71, and 72 respectively.

TABLE 21 Acetone and isopropanol produced from various combinations of genes Acetone Isopropanol Organism Substrate (g/L) (g/L) Clostridia genes pMTL85147-thlA-ctfAB-adc E. coli Sugar 0.200 N/A C. autoethanogenum CO 0.300 0.025 C. ljungdahlii CO 0.180 0.005 pMTL85147-thlA-ctfAB-adc-sadh E. coli Sugar 0.080 0.070 (C. beijerinckii) pMTL85147-thlA-ctfAB-adc-sadh E. coli Sugar 0.060 0.080 (C. autoethanogenum) Novel genes pMTL85245-kivd-adh2 E. coli Sugar N/A N/A C. autoethanogenum CO Detected by 0.050 GC qualitatively pMTL85245-kivd E. coli Sugar N/A N/A C. autoethanogenum CO Detected by 0.064 GC qualitatively Combination of Clostridia and novel genes pMTL85147-thlA-ctfAB-adc-kivd E. coli Sugar Detected by N/A GC qualitatively C. autoethanogenum CO Detected by 0.091 GC qualitatively pMTL83147-thlA-ctfAB-adc-adh2 E. coli Sugar 0.040 N/A C. autoethanogenum CO Detected by 0.648 GC qualitatively pMTL83147-thlA-ctfAB-adc-P- E. coli Sugar 0.076 N/A kivd-adh2 C. autoethanogenum CO Detected by 0.043 GC qualitatively

Tolerance to Acetone and Isopropanol and Detoxification of Acetate in Acetogens

Several metabolites such as alcohols (ethanol and butanol) or acids (acetic acid and butyric acid) are known to be toxic for bacteria in high concentrations and thus limit their biotechnological production [Alsaker K V, Parades C, Papoutsakis E T: Metabolite stress and tolerance in the production of biofuels and chemicals—systems analysis of butanol, butyrate, and Acetate Stresses in the Anaerobe Clostridium acetobutylicum. Biotechnol Bioeng, 2009, 105: 1131-1147]. To see if acetone and isopropanol have a toxic effect on cultures, growth experiments were carried out in 50 ml PETC media (Tab. 2) in serum bottles, adding different concentrations of acetone (FIG. 12) and isopropanol (FIG. 13) to growing cultures of Clostridium autoethanogenum DSM23693. Cell growth was visible in presence of concentrations as high as 5% acetone or isopropanol (with only slight inhibition of growth rate).

A high concentration of free or undissociated acetic acid on the other hand is known to be detrimental for most anaerobic bacteria (including acetogenic bacteria) due to the deleterious effect on the membrane gradient [Warnecke T, Gill R T: Organic acid toxicity, tolerance, and production in Escherichia coli biorefining applications. Microb Cell Fact, 2005, 4: 25; Köpke M, Dürre P: Biochemical production of biobutanol, in Luque R, Campelo J, Clark J H (Eds.): Handbook of biofuel production—Processes and technologies, Woodhead Publishing, Camebridge, 2010: 221-257]. Acetogenic bacteria however, need to produce acetic acid to gain ATP from substrate level phosphorylation [Drake H L, Küsel K, Matthies C: Acetogenic Prokaryotes. In Dworkin M, Falkow S, Rosenberg E, Schleifer K H, Stackebrandt E (eds.): The Prokaryotes, 3^(rd) Edition, Volume 2, Springer, New York, 2006: 354-420] and thus all known acetogenic species produce acetic acid [Drake H L, Küsel K, Matthies C: Acetogenic Prokaryotes. In Dworkin M, Falkow S, Rosenberg E, Schleifer K H, Stackebrandt E (eds.): The Prokaryotes, 3^(rd) Edition, Volume 2, Springer, New York, 2006: 354-420]. Conversion of acetic acid to other products such as ethanol via aldehyde ferredoxin oxidoreductase (AOR) or back to acetyl-CoA via phosphotransacetylase/acetate kinase (Pta/Ack) or AMP-dependent acetyl-CoA synthase (Acs) is unfavourable, since it requires energy in the form of reduced ferredoxin or ATP [Wolfe A J: The acetate switch. Microbiol Mol Biol Rev, 2005, 69: 12-50]. This invention presents a novel mode of acetic acid detoxification in acetogenic bacteria, which is free of energy requirement. Acetic acid can get recycled back to acetyl-CoA via a Acetoacetyl-CoA:Acetate/Butyrate Coenzyme A transferase system consisting of Acetyl-Coenzyme A acetyltransferase, Acetoacetyl-CoA:Acetate/Butyrate Coenzyme A transferase A, Acetoacetyl-CoA:Acetate/Butyrate Coenzyme A transferase B. This reaction drives the conversion of Acetoacetyl-CoA to Acetoacetate, which can then get decarboxylated to acetone and reduced to isopropanol (FIG. 4).

The invention has been described herein, with reference to certain preferred embodiments, in order to enable the reader to practice the invention without undue experimentation. However, a person having ordinary skill in the art will readily recognise that many of the components and parameters may be varied or modified to a certain extent or substituted for known equivalents without departing from the scope of the invention. It should be appreciated that such modifications and equivalents are herein incorporated as if individually set forth. Titles, headings, or the like are provided to enhance the reader's comprehension of this document, and should not be read as limiting the scope of the present invention.

The entire disclosures of all applications, patents and publications, cited above and below, if any, are hereby incorporated by reference. However, the reference to any applications, patents and publications in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that they constitute valid prior art or form part of the common general knowledge in any country in the world.

Throughout this specification and any claims which follow, unless the context requires otherwise, the words “comprise”, “comprising” and the like, are to be construed in an inclusive sense as opposed to an exclusive sense, that is to say, in the sense of “including, but not limited to”. 

1. A method of producing acetone comprising culturing a recombinant microorganism in the presence of a gaseous substrate to produce acetone, wherein the recombinant microorganism comprises an exogenous thiolase (EC 2.3.1.9), an exogenous CoA transferase (EC 2.8.3.9), and an exogenous decarboxylase (EC 4.1.1.4 or EC 4.1.1.74).
 2. The method of claim 1, wherein the recombinant microorganism is a carboxydotrophic and acetogenic bacterium.
 3. The method of claim 1, wherein the recombinant microorganism is derived from a parental microorganism that does not produce acetone.
 4. The method of claim 1, wherein the parental microorganism is a microorganism that occurs in nature or a microorganism that has been previously modified.
 5. The method of claim 1, wherein the recombinant microorganism is derived from a parental microorganism that lacks a gene encoding alcohol dehydrogenase.
 6. The method of claim 1, wherein the recombinant microorganism is derived from a parental microorganism selected from the group consisting of Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium ragsdalei, Clostridium carboxidivorans, Clostridium drakei, Clostridium scatologenes, Butyribacterium limosum, Butyribacterium methylotrophicum, Acetobacterium woodii, Alkalibaculum bacchii, Blautia producta, Eubacterium limosum, Moorella thermoacetica, Moorella thermautotrophica, Oxobacter pfennigii, and Thermoanaerobacter kiuvi.
 7. The method of claim 1, wherein the recombinant microorganism is derived from a parental microorganism selected from the group consisting of Clostridium autoethanogenum, Clostridium ljungdahlii, and Clostridium ragsdalei
 8. The method of claim 1, wherein the thiolase is Clostridium acetobutylicum ThlA or Clostridium beijerinckii ThlA.
 9. The method of claim 1, wherein the CoA transferase is Clostridium acetobutylicum CtfA and CtfB or Clostridium beijerinckii CtfA and CtfB.
 10. The method of claim 1, wherein the decarboxylase is acetoacetate decarboxylase (EC 4.1.1.4).
 11. The method of claim 10, wherein the acetoacetate decarboxylase is Clostridium acetobutylicum Adc or Clostridium beijerinckii Adc.
 12. The method of claim 1, wherein the decarboxylase is alpha-ketoisovalerate decarboxylase (EC 4.1.1.74).
 13. The method of claim 12, wherein the alpha-ketoisovalerate decarboxylase is Lactococcus lactis KivD.
 14. The method of claim 1, wherein the gaseous substrate comprising one or more of CO, CO₂, and H₂.
 15. The method of claim 14, wherein the gaseous substrate comprises 20-70% CO.
 16. The method of claim 1, wherein the gaseous substrate is derived from an industrial process selected from the group consisting of ferrous metal products manufacturing, non-ferrous products manufacturing, petroleum refining, coal gasification, biomass gasification, electric power production, carbon black production, and coke manufacturing.
 17. The method of claim 1, wherein the gaseous substrate is syngas.
 18. A recombinant microorganism for the production of acetone comprising an exogenous thiolase (EC 2.3.1.9), an exogenous CoA transferase (EC 2.8.3.9), and an exogenous decarboxylase (EC 4.1.1.4 or EC 4.1.1.74).
 19. The recombinant microorganism of claim 18, wherein the recombinant microorganism is a carboxydotrophic and acetogenic bacterium.
 20. The recombinant microorganism of claim 18, wherein the recombinant microorganism is derived from a parental microorganism that does not produce acetone. 